Stacked sound change?

Hello List,
here's a funky idea which occured to me recently:

If a language had a sound change X->Y going on that in several environments
(IF A), (IF B), is there any chance that the results would be cumulative
(X->Z) in case of (A AND B)??

Example: historical sound changes changed English /&/ to /O/ before /l/ and
after /w/ ("war", "fall"). "Stacking" would here mean approximately "wall"
becoming /wUl/ rather than /wOl/.
Note that the following analysis
1) /&/ -> /O/ if before l or after w
2) /O/ -> /U/ if between w and l
would *not* be possible, since a stacked sound change would ONLY apply to
older /w&l/, not hypothetical older /wOl/.

Does this sound the least bit plausible?

---

If not, how about cumulative results of two different sound changes? Example
#2 follows.
Assuming that /d/ and /tS/ already exist:
/t/ -> /tS/ before /i/
/t/ -> /d/ between /n/ and a vowel
so /t/ -> /dZ/ between /n/ and /i/
while /ndi/ and /ntSi/ remain intact?

John Vertical

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