Can you be baptized a Christian then again as a Roman Catholic?

First off, Catholicism is the first and foremost Christian religion as founded by Christ. As to your question, you can only be baptized once. If done properly, the Catholic Church recognizes the baptism as valid. If the Church is uncertain if a person was validly baptized, that person will receive a conditional baptism. "If you were not baptized before, I baptize you in the name of . . . ."