It takes 90 days from application to get a GRC but yea they could, provided they also got a new birth cert per the club rules and claimed satisfied the rule for " issued at birth".
However that would be where the legal challange would start.
The IRFU have no legal right to ask for a GRC. The only time a GRC has to be produced is when there is a legal obligation, and filling in a club application form would not qualify. So they have to rely on yee olde tell us if "you have a penis, or had a penis my dear" check. So then it becomes, what happens in the ga game situation? The one side points out that the other club has a (ex?)bepenised on the field has the ref the obligation to stop play? Can he or she be sued too?