Any “voter” can register however they want. But the RNC will decide who the RNC will run as a candidate under the RNC banner.
Considering the fact that the RNC's support has gone heavily to liberals in the party over the last decade, that's hardly encouraging. Especially in light of the fact that the "conservative" they've now chosen to lead the RNC is a co-founder with Christie Todd Whitman of the "Republican Leadership Council," whose purpose is to forward pro-abort, pro-homosexual agenda, anti-gun, anti-liberty, leftists.