RMX, Assistant and CSTA hotfixes work fine with or without SLES update license.
Only PLT platform (i.e. SLES/Linux) hotfixes can not be applied when SLES update license is missing.
And yes, RMX moves and changes can be completed, no problem. RMX moves and changes have nothing to do with SLES update license.
If you have a V6 4K which has M44 status, then no PLT HF's should be coming anymore anyway, so SLES update doesn't matter.
For a V7/V8 4K, it's probably worth getting the license, because security updates etc will be coming through PLT HF at some point.
You need 1 update license for each SLES platform install. So simplex - one license. Duplex - two licenses. Duplex with 2 APE's - 4 licenses in total. The license does not need to be applied to APE, it's done on the main host Assistant only.