See erikharrison's post. Just a quick comment from me: your code first tries a match and then a substitution which has to find the same match again. It is ok to try substitution on strings where the match would fail - the result will simply be no change. You can just remove the if:

while (<$FRAME_FILE>) {
    s/$change_on/$change_off/g;
}
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or simpler s/$change_on/$change_off/g while <$FRAME_FILE>; In fact, you can use substitutions in conditions as well:

if(s/$change_on/$change_off/) {
   ...
}
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The block will only execute if a substitution happened.

Makeshifts last the longest.