>>>Am I correct in assuming that you reserve the term pun for those bon mots that use alternative spellings of words with the same pronunciation to invoke a groan from the audience?

Gotta tell you folks, Puns, SDS, word switcheroos...they ALL make us groan. We just shake our heads, mime "cuckoo-puffs" to one-another while pointing this way, and carry on as if nothing ever happened.