Convert rca cable into xlr cable.

Depends. For balanced connection through XLRs, you need at least 3 conductors (+/-/G) but for unbalanced through RCAs you need only 2 (+/G). So, if by some chance your RCA cables have 3 conductors or more (many do), you can do it. Otherwise, no.

Kal

If the equipment having an XLR connector is capable of using a single ended electrical signal (and many are) you can change from RCA to XLR. However the electrical interface will still be single ended. I have some cables with RCA on one end and XLR on the other. The Behringer DEQ2496 which gets the XLRs automatically detects that the input is single ended, and adjusts its gain accordingly.

You need to ask the cable manufacturer. I have had both Cardas nd Harmonic Tech cables re-terminated to XLR, but could not have it done with some Wireworld I once had.