I need to work on my shower fixture but the walls are made of fiberglass and it seems it's a wall sorround one piece. Is there a way of working on this type of walls without braking or cutting it?

Can you work on it from behind the wall? You can make an access panel for future repairs.

If you can't cut an access panel from behind as suggested by Rusty50 then you may be able to use a REMODELER PLATE (see images), but that will require some cutting of the surround, some special tools (mini-cutter), and some good soldering skills... ;)

Exactly what issue brings you to ask this question? Perhaps we can help you to repair the existing shower valve, maybe? Let us know more, OK?

Mark

Using the process outlined by Rusty50 is usually the best approach if possible. Many new home construction designs put the shower controls on accessible closet walls. My house has 3 baths and all of them are backed to a closet or utility space. Install a removable cover and no one will know!

You will have to cut a wall, hopefully you have a sheet rock wall behind the faucet, if so that is where you would want to cut. Unfortunately you will have to cut something. Are you replacing a faucet or repairing it?