Was it J. Michael Straczynski who suggested swapping the two episodes, or was it ABC?
I think it was Straczynski. He wrote “Slimer, Is That You?”, and probably requested that ABC swap it with another episode so that more of his scripts would be shown for the new season.
The boxset it was noted on atleast one of the interviews.
When JMS left the show over the changes, DIC swapped the episodes to give season three more JMS writing. Ultimately, They got JMS to write one episode for the season towards the end. Slimer, Is That You? aired as a Saturday morning episode despite it being the old designs because of it. Transylvanian Homesick Blues was then aired at the end of Season 2 instead. Note that there are two audio recordings of Slimer, Is That You?. International airings of the english got the original version while America/Canada got a redub.
Someone speculated that there might be a version of “Transylvanian Homesick Blues” with Laura Summer and Lorenzo Music tucked away in a vault somewhere. I doubt there is, because of two things:
Slimer has his “Slimer-Speak” that he had in ABC Season 2 and beyond.
Slimer has a tail in some shots, despite having his original design for the most part. (the rounded bottom)
“Transylvanian Homesick Blues” is Animated as a Season 3 with the designs. So it was never voiced as a season two. However, thinking about it, the episode has two element that may have warranted it to be moved to the weekdays… The big red flag is the gun the villain threatened the ghostbusters with in the episode. Second, they were avoiding the topic of death seasons 3 and on, so a Vampire that is noted as such including a line from Egon saying he is the Undead is probably going too far for Saturday. So the episode is not written as a season 3 episode cause of that.