Isn't it mandatory to do a wheel alignment after and control arm replacement?
The proper answer would be yes. I have however replaced upper control arms and gone about my business. It is my opinion that if you don't remove the lower controls from the sub-frame of the car, and or don't loosen the nut that allows for adjustment on the tie rod ends, everything should go back together the way it came out.
Here is my methodology behind this thinking:
Upper control arms have no adjustment (at least OEM ones).
All other attachment points are either tapered pin or straight pin with fairly precision locating. Which includes the upper control arms, both lower control arms at the bottom of the knuckle, and tie rod ends.
If you don't adjust the tie rod ends the toe in / toe out adjustment should remain the same.
If you don't loosen the lower control arms at the sub-frame then those never change position.
Camber and caster are essentially built into the OEM suspension leaving only toe in / toe out adjustment, which is adjusted only by the tie rods.
My '98 GLS (my daily driver) has had the steering / spindle knuckles completely removed from the car since I originally installed a complete refresh of Febi / Bilstein front suspension components.
I replaced both my CV axles and re-assembled everything and went down the road. That was 2 years ago, and my front tire wear is pretty damn even.
However, if the car at some point had a front end alignment done with worn components, either to bring it back into spec or for whatever reason(s) then all bets are off.
Then I would most certainly take it in to make sure everything is aligned properly.