CAN YOU DOUBLE BACK OR RETURN TO CITY OF DEPARTURE

Folks have a bit of a dilemma and , finding no real info , so I'm hoping someone can tell me..... We are Irish Citizens ,So not the Own country rule....So We have interrail passes , now let's say We go from Florence to Rome and need to return to Florence that evening....so a day trip, then the next day , let's say go from Florence to Venice ,and return back that evening.....With Florence as a possible base.....is this allowed or classified as commuting, even tho not actually commuting....??? I have seen posts online, where people were Told by train conductor this was not allowed and invalid as can't do return.....the posts seem to be a good few years old , Now I was thinking, Maybe book as singles , so using examples above, but making individual seat reservations for outbound and inbound....I hope I'm making Sense....OR DO WE NEED TO WORK IN A LOOP FORMAT, Only using any given city once , which tbh will be a logisical nightmare.....not ness those actual destinations, just using as an example to explain...... Really hope someone can help that HAS ACTUALLY DONE THIS....many thanks in advance