quickie about suffix terminology

My conlang (Wenetaic) has two classes of root-suffix, those that accept
morphological modification, and those that don't.  The order within a word is
always:

root+modifiable.suffixes+unmodifiable.suffix
There are zero or more modifiable suffixes per word, and either zero or one
unmodfiable suffix.

I'm currently using "particle" and "suffix" respectively for these two types of
suffix, for historical reasons.  This does not sit well, however.  Does anybody
have a suggestion for a "professional sounding" terminology I can use?  I'd
prefer something quicker and easier to type than "modifiable suffix" and
"unmodifiable suffix".



Thanks


Paul




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