you need morphophonological rules for merging so like if there's a rule that an initial V or VC syllable is eliminated from the first word of a compound and a rule that in a compound the stress comes from the longer word, then say you have ahi + kutekaŋí, it would become hikųtekaŋí
or in the case of ponani and kujuk, it would become ponanikųjuk with the rules i've established here, you could also have lenition or debuccalization of /k/ at the morpheme boundaries so that the final result of ahi + kųtekaŋí is hithųtekaŋí. with all those rules, ponani + kujuk would become ponanithųjuk
btw himalian has no morphophonologicL processes except for inserting a glottal stop to separate illegal vowel diphthongs or triphthongs and inserting a schwa to separate illegal consonant clusters