When these episodes first aired, did anyone think that this was set up for Jonathan Frid to leave DS and another actor to play "Barnabas" in a different body? 

When I first watched these episodes on New Jersey Network in the 80's with my brother, that is what he thought.  He didn't know about DS other then the episodes he was watching.  I was sort of like that too, but knew enough about the show that this wasn't the case.

At least, with the exception of one episode in 1840, DC never brought Addison Powell back again to DS.

Here are pages 3 & 4

The Secret Room front & back covers

I finally went looking and found the article.    Here it is in full:

WHY I THINK DARK SHADOWS ATTRACTS GAYS AND OTHER MINORITIES.

Many characters on Dark Shadows fall into minority groups.  many of these people are in minority groups due to an affliction they have, whether it be vampirism, werewolfism, possessions, etc.  Many of the fans seem to be able to identify with these characters for whatever affliction they may have, or for whatever minority group they may belong.

Certainly handicapped people & obese people feel the affliction mentioned above,  If they could cure their blindness, eating disorder, paralysis, etc., they could live normal lives, and these very people see that if the characters could cure their vampirism, werewolfism, etc., they could have normal lives as well.

Gays I think tend to identify with Barnabas for many reasons.  Here is a man who may not like what he is but has to submit to it.  I think many gay people feel the same way about their sexuality.  he is a man that despite what he is has been able to gain the love, trust, & friendship of all those around him even the ones who know of his "secret". gays have a "secret" and they long for the kind of relationships Barnabas has with his family.  The want the acceptance he is able to have, despite what he is.  Barnabas is also a hero.  He is able to overcome his "problem" to do great things.  he is also able to achieve almost all of his goals, or nearly so, that he is successful, even if his goal is just barely missed being 100% achieved.  Something we can all identity with.  And love... Barnabas Collins & love.  Gays I think are really identified with this aspect.  gays are not known for their long term relationships.  Of course this sometimes happens, but often as not our love affairs do not last that long.  Neither do Barnabas'.  For one reason or another, often due to the actions of others, he loses the love he has sought.  he loses it, & we can not only identify with what he is feeling, but often by the same actions.  How often have we felt we have lost the love of our lives due to someone else's actions?  Yet, barnaba is able to go on with his life, for better or worse, & i think that is something we all wish we could do, or at least hope we are doing.

I also think the fans identify with the ones who get hurt, are taken away, the object of someone else's love, & we, like them, swept away like Josette, etc.

Certainly the gays & handicapped alike envy Angelique.  What we could do if we had her powers!  We could make ourselves whole.  We would be cured.  We would destroy our enemies.  We could get the ones we love.  Then again, Angeliques' power betrays her, & she winds up not getting what she desperately wanted.  How many of us feel this way?  That no matter what lengths we went to, no matter how good we planned, things for one reason or another just didnt work out & we get screwed in the end.

Gays will certaily feel affinity for Elizabeth Collins Stoddard, hiding that "secret" for 18 years.

And what of Julia Hoffman?  Certainly gays know what she must be going through every time she looks at Barnabas with those "I love you" eyes & he simply ignores her.  Don't we all have stories like that to tell from our own lives?  You do everything in the world for a person & they ignore the fact that you love them.  And what of the other side of the coin?
Barnabas is fully aware of how Julia feels, and yet he ignores it because he she is just not exactly what he is looking for in a relationship.  He is not attracted to her.  He has been hurt by another lost love and has not gotten over that.  He thinks the world of Julia and would do almost anything for her; she is his greatest friend, but...love, the way Julia wants it, is never to be...probably.  I think many gays have this sort of thing in their lives.  There's always someone who wants you that, even though you may be desperate for love yourself, you simply are not attracted to them in that way, & probably never will be.  Perhaps you will be someday when you have gotten over the broken heart you're nursing from your lover of three years ago, but certainly not now.

These are some of the main reasons I feel that DARK SHADOWS attracts gays & other minorities.  The show may have bad sets, at times horrific make up, blown lines, sorry acting, shitty video quality, but what has always attracted the fans has been the mood, the tone, the writing, THE STORY.  There's the ticket.  The Story.  We see things in it that reflect things in our own lives, often to a frightening close proximity.  I think handicapped persons & gays especially fall into thses categories for some of the reasons listed above.  These groups often fall into fandom of T.V. shows & movies, but a high number to seem to be attracted to DARK SHADOWS.  I think the show not only lets you escape from your own world, but lets you live out part of your world in a way you wish you yourself could.

Thats why the original series worked so well, as there wasn't any prior DS series to go by, so they were able to start fresh and slow.  First, by the regular Collins characters for the first 10 months and then the development of Barnabas, and later Julia, over the next 8 months before they decided to show an origin in 1795 that was for five months. 

Being a daytime soap allowed them a lot of trial and error to get it right and by doing that trial and error, we got to get really involved with these characters for the long run.

In the early episodes it was hinted that he was able to turn himself into a dog.