Not really, although Jobs were never originally planned in FFXIV's design (Tanaka even said he wanted to keep away from the traditional FF jobs in FFXIV) there was a musketeer class designed for the Alpha of 1.0. Musketeer even has an unused guild in Limsa and looking at the types of weapons GLA uses there are no rapier, epee, or other fencing type weapons in GLA's arsenal or in the game at the moment.
Besides that, functionally GLA to RDM does not work in the slightest. You'd be pushing a very defensively focused class into a magical DD focused environment, who would only have the lowest tiers of magic from their cross-class abilities and have little to go off of outside of their job specific actions to strengthen itself.