Most likely, no.
If you are replacing the LNB on a Slimline dish, you shouldn’t have to re-aim it. Older dishes should probably be replaced completely instead of just replacing the LNB.
Why would you want to replace the LNB? In the past you probably did it for an easy upgrade to DIRECTV SWM technology. These days, you’re probably putting up the new Reverse Band 3 LNB so that you can be ready for future 4K channels that (hopefully) are expected to appear in 2018.
What’s the best way to avoid having to re-aim the dish? Before you start, mark the position of the tilt, elevation and azimuth markers on the dish with a pencil. This way if you accidentally knock the dish out of alignment, you’ll know. And of course, be very careful in how you remove the old LNB and attach the new one.
Looking for a more detailed tutorial on upgrading your dish? Click here.