RT, as I understand it the answer to your question: ” how could Amram “re-marry” Yocheved if he may have had the din of a Cohen? ” is as follows: At that time in Egypt, before the Torah was given, our ancestors had the status of being Beni Noach and therefore this was permitted. The prohibition of a Kohen marrying a divorcee only applied to Jews.
In addition, you might also ask an even more fundamental question: How could Amam have married his aunt, Yocheved as this is a forbidden relationship for Jews? The answer, as I understand it, would be the same- The marriage of an aunt to a nephew is permitted for a Bnei noach and is only forbidden for Jews and pre-Torah our ancestors had the status of Beni Noach. The definite proof that this marriage (and remarriage) was absolutely permissible is the Gemara in Tractate Shabbos that states that only 4 people died as a result of the sin in Gan Eden, as they never sinned themselves. Amram is one of those 4 persons listed.