Can you merge a 5*+10 unit?

So as a person who likes to min/max things, one of the reasons I've been hesitant to merge 5* units is because the "optimal" IVs for characters might change as more updates, weapons and skills are released and I was afraid that hitting that +10 status would prevent me from changing that units IVs ever again.

But then I thought: Can you merge a 5*+10 unit into another one? Like if I later on pull a copy of that character with better IVs, can I merge my 5*+10 unit into it and start building merges again on the new one or is the 5*+10 unit locked to stay that way forever stat-wise?