I am sorry Kirakiraさん, I must have not explained myself very well. I already knew what you explained, but what I meant is something else.
Unfortunately the only 2 example that come to my mind are not 100% the right sample for my question, but I will try anyway. Take Japan: 日本 which can be read にほん or にっぽん. I understand this is a case of phonetic adjustment, but there are case where the readings are completely different yet keeping the same meaning. Another example (but even this case won't work perfectly because the meaning is not 100% the same) is 一寸 where you can say it ちょっと or いっすん.
I can't think of more appropriate examples...sorry
