Gosh I notice these room changes all the time. I know the Blair house that Nickolas uses now is exactly the same as they used for Dr.Lang's residence. From the staircase, the main room & the front door, it's all situated just as Dr.Lang's residence was. They seem to use this set up quite frequently on the show. I've also noticed that the main room looks to be the same one as they used for Naomi & Joshua's bedroom during the 1795 storyline.
Another room that is frequently used is Angelique's old bedroom from 1795. I can always tell by the window that is there in that room. There's a kind of slant right above it so it quite noticeable.
You're right about the fireplace being new in Julia's room as this is the first time that I've seen it there.