Say I have to edit an appvar.

I can do that:
Unarchive it.
Edit it.
Archive it.

The problem with that is that I can lose all my progress if a RAM Clear occurs for some reason (like battery dead).

So I would like to do that:
Copy appvar to temporary one.
Edit temporary appvar.
Delete original.
Rename temporary with original name. ←
Archive renamed appvar.

So how do I rename an appvar (that is in RAM if that helps) ?

It's a very painful process, and it requires ASM. Theorically, you have to find the address of the VAT header of your appvar (let's say you stored it in P), put the new name length into {P-6}, use _insertMem or _delMem at P-7 depending on whether the new name is longer or smaller than the previous one, and then write your new name from P-7 to P-7-{P-6}+1.

Thanks. And if I smartly chose the name of the temporary appvar so that it has the same length as the original one, length is not an issue.
Now how do I get to the VAT header of the appvar (I have its name to find it but that's pretty much all) ? Is there another way than going through the VAT and Equ►String-ing everything ?

I did that a lot with Calcsys and its hex editor, provided it's the same length. Or else Doors CS might have a rename function I dunno.

Okay so my investigations led me to something interesting : you can retrieve the pointer to the VAT header of a variable given its name with GetCalc(name [,size])Asm(EB)->P. I'm trying to write the actual code you need.

Learn asm in 28 days actually has a page on the VAT. Using that info and matrefeytontias's trick you should be able to rename it.

Basically take the VAT pointer, subtract 7, and then write the name backwards. Make sure the program is in RAM though, otherwise when you unarchive it, bad things happen. (I don't remember specifically what, but I remember you don't want it to happen.)

It's actually not a problem with unarchiving, but having a disconnect between the real VAT entry and the copy in archive when a Garbage Collect occurs. Unarchiving afterward actually prevents problems in this case, because the incorrect entry in archive is then marked for deletion. The garbage collector takes the name from the archive copy and ChkFindSym's it to update the VAT entry in RAM, but if the name doesn't match, the entry never gets updated and it points to an invalid spot in archive, showing crazy sizes or error in the memory menu. In addition, the OS doesn't check whether it exists or not after searching, so it writes the new pointer to a particularly volatile spot in RAM that causes a crash the next time you get an OS error. Really bad stuff.

I have a problem, even with fixed length. Here is what I try to do for now:

Get size of archived appvar to edit works
Create temp appvar and keep the pointer to its VAT entry works
Copy content of original in temp works
Edit temp works
Delete original works
Rename temp using the pointer I kept doesn't work
Archive temp doesn't work (of course, I try to archive with the wrong name)

I think that the "Delete original" part changes the pointer to the VAT entry of the temp appvar so the one I kept is wrong, and the following "Rename" part renames nothing. Is that true ? How do I fix it ?

edit seems like (after some disassembly) using MEMKIT to look for the appvar knowing its name, then using "Print" and "ex hl,de" returns the pointer to the last letter of the name of the appvar... I'll try that this afternoon.
edit2 seems to work