1. No, it is not necessary to do a SWAP and COMPLEMENT unless this is what you want to do! I would guess that the code you are referring to is probably doing a 4bit interface to a LCD, in which case you do a SWAP to get the high 4 bits into the low 4 bits. As for the COMPLEMENT, we'd need more information to make a judgement.

2. multiplexer and demultiplexer and two separate operations, it is sometimes shortened to mux and demux.