I have an 04 tl and like the sound system ok and the stock look a lot but i like the 07 deck which has mp3 and aux input and is identical in shape (at least it looks identical in shape)

can they be swapped?

 

Yes, if you want to spend alot and do alot of work. If you TL is a Navi TL, then you will need to replace the following:
Nav DVD drive 2K
HeadUnit
Nav Screen
XM tuners
Wiring changes
XM antenna
HFL unit

if non-nav, you will need to do A LOT of fab work

Retrofit 07+ non-navi center stack into 04-06 stack
Replace Radio
Make necessary wiring changes
Replace XM tuner
Replace XM antenna
Replace HFL unit

If you just need an Aux input, get the 150 dollar USA SPEC or DICE unit, these also support IPOD's so you get the MP3 feature as well, easiest thing to do.