We're on public cloud, and our current interfix string is the platform ID. While there's nothing "systematic" that breaks with the interfix, it's certainly long and I'd love to shrink it a little just to have fewer characters and overall shorter. 
 

I'm thinking a 3-character code for our org would be fine to keep an interfix, but significantly shorten it. 

Are there any considerations about changing the interfix after having a fairly significant amount of items created with the current interfix? Does having "old" and "new" interfix strings break things fundamentally? Is this a bad idea altogether and not worth contemplating at all?
 

It seems like the value in it is to be able to exchange data with other platforms and not have naming conflicts, which sounds reasonable. How many characters should I have to be reasonably confident of not clashing? Also, this might be a vanishingly small chance of collision and not worth worrying about. 

Another thread on interfix for "General guidelines" which states that it shouldn't be blank, which I'm okay with maintaining: