need to change copper pipes when changing A/C compressor unit?

It's best practice to install new line-sets but in your case where the lines are buried in a concrete wall, the HVAC installers *might* flush the lines and reuse them.

Best practice is to replace them. What is holding them in the concrete? Often they are in a sleeve of some sort so they can be replaced. Copper should not be in contact with the concrete as over the years it can cause corrosion and leaks.

My guess is the installer has run into this before and knows what to do.

As long as they are in good shape and of the correct size for the new unit.

Needs to be replaced, why? The why helps determine if the copper tubing should be replaced.

The copper tubes are for refrigerant. Freon is a brand name. The tubes may carry Freon, Isotron, Genetron, Forane, or some other brand of refrigerant.

If they are not corroded and are the right size, no reason to replace. When I replaced my outer unit, it was originally a threaded fitting and the new unit was a braze-in so I just cut off the fittings and brazed the lines to the new unit.

So purge the lines. We purged my entire unit with compressed air first, then nitrogen before evacuating and recharging.

If the lines are 40 years old, but they've never lost their charge, they might still be not corroded and usable???

(Mine are 36, but I'm planning ahead. Last 2 years, no AC. This year, portable AC that works quite well, doesn't make enough noise to bother me (which surprises me). What bothers me is having the window shut and the bedroom door shut. I've only needed it 6 times so far this summer, so no rush about the central air, yet I know I'll want to fix it eventually..)

Yes, they might not be corroded or then again they might. Take your pic. Which is why most installers put in a new line set. They only cost $200 for a typical run. If they are inside an inaccessible location, like running vertically inside a wall, and they look in good condition, then installers will flush them and re-use. Some installers will re-use them anyway to keep the price down.

I was planning to replace them, but just wanted to be prepared if that turned out to be "impossible". If someone said, even if they look good, at that age, they are sure to be no good, I'd find osomeone to do the "impossible"