[MRM]

"Slim" coat obviously autocorrected from skim coat.

That's a nice vintage house. You don't need or even want all of the stucco to match patina perfectly. It will look unnaturally sterile and contrived if you do. Leave all of the original stucco as-is, patch the replacement stucco as closely as possible but don't sweat the details, and install the new stuff proudly as new stuff, showing that it has new, old and everything in between stucco.

If there is paint on the existing stucco, the only way to remove it is sandblasting. If the paint isn't causing a moisture intrusion issue, then it's working on that application and shouldn't be messed with. If it is, your builder will have found that our and removed it. Just leave the current stucco as-is, patch in the new patches matching as closely as possible to the original and try to match the new stuff to the old. It won't match perfectly (new and old stucco never quite match) so chalk it up to the character of your house and wear it as proudly as the owner of a survivor 356 B cabriolet would wear every crease and dent on his pride and joy.