It's done every day. There's no need to touch the brick. Replacement windows can be ordered to fit almost any size opening, old or new. If you do have one or two oddball windows, custom sized replacements can be made.

How the old windows are removed and the new ones installed is a judgement call for the installer. Most times, windows are removed and replaced from the inside, but, now and then, it's best done from the outside.

Is the house masonry (no studs in outside walls and bricks 2 thick) or brick veneer (frane house with 1 layer of brick?
Brick veneer is done the same as a frame house since there is wood to attach the window to.
Very few installers will do masonry except by placeing the new window inside the old window frame (this gives then wood to fastern to). This also makes you lose about 2-3 inches of window in width and height.
A better method is to install 3/4 inch thick buckboards lining the opening and then install the windows.
The best method is to fasten the new windows into the masonry using tapcon or other fasteners and polyurethane caulk. Enough fasteners to hold things till the poly caulk hardens up.

We had 24 windows replaced in our brick home and you would be surprised how easily the old windows come out. No damage inside or out.

Texasredhead, what kind did you replace with? Regards, PK, ps, I am in La.

We had a similar concern when we had to replace a Pella window in our home. It's best if you can use the same contractor that built the home/installed the window or if you have pictures showing how the window was initially installed. We used a different contractor and he was done in one morning. Charged me $98 labor (Nebraska)

Not possible to use the same person, we are going to do ourselves, couple at a time, now to choose the window......................... pk