Getting ready to pull the engine, what to do with AC system? All tips taken...
 

Do you have to discharge the system, or can you unbolt the compressor off the block and hang it? Any other special tips that might save some headaches?

Have the system discharged. You shouldn't disconnect the A/C components and hoses until the system has been dischaged.
-Joe

How do I get it discharged without having to tow the non-running car someplace?

I think you have to have proper discharging equipment to do so.
-Joe

Use or borrow a AAA card.

You are fixing this car right? this motor or another is going in right? If the answer is yes pull the lines out of the way and tie them up. If the anwer is no. THen the legal answer is have it discharged in a proper manner.

This is what I do.

I did this with 2*W123 300Ds I swapped the engines on. It was an easy solution to a potentially problematic issue. I pulled the radiator but left the condensor in location during the work and I put a piece of ply between the condensor and the engines while pulling & replacing the engines.
The A/C on both cars worked well afterwards.

NOTE: There are 3 spacers between the compressor and engine which are 3 different sizes. Take measurements of them as you remove them, so you can put them back in the right place. Do not let them fall out, it is a PITA to swap them around to get them right again.

Thanks for all th prompt tips, it's actually the same engine going back in with a different tranny, and now that I'm really looking at it, I never used the A.C. as it had no belt on it, and I'm not even sure the line's to the condenser are hooked up! After I got this one I realized it had been wrecked and repaired, maybe the guy never recharged the system. Good to know I can go ahead with just demounting the compressor... thanks again.