How to replace a concealed flush cistern

[Altavista]

I live an area with very hard water and this has resulted in the flush mechanism in the cistern on one of the toilets in the house to seize up. The actual flush itself has never been a very convincing affair. I am now considering changing the entire cistern and/or flush mechanism. The problem is that the whole lot is concealed behind a plasterboard wall. When I do replace I am planning to incorporate an access panel so I can get to the cistern with more ease. The current setup is shown below

I plan to do the following

1. Cut the plasterboard around the current opening to create a nice rectangular access area - say 40cm wide and 25 cm high.
2. Access the innards, take out the current flush cistern, install a new one
3. Place diagonal wooden battens in the four corners (from the inside)
4. Get a nice decorative piece of plexiglass/acrylic, cut out a hole for the actual flush knobs
5. bolt the plexiglass to the diagonal battens with decorative stainless steel screws

However, plumbing is not quite my area of expertise and I have not done this sort of job before. Are there any do's and don'ts here that I should be aware of? Or am I thinking this all wrong? I'd much appreciate any help and tips.

 

[Terry]

If this is an in-wall tank, they sometimes have a flush button panel to can be lifted up and away from the wall for access to the fill valve and flush valve.

 

[Sponsor]

 

[Altavista]

Y
If this is an in-wall tank, they sometimes have a flush button panel to can be lifted up and away from the wall for access to the fill valve and flush valve.

The issue I have is just that - there is no access panel or anything similar that I can use to replace anything in the flush. The flush mechanism has seized up entirely thanks to the hardness of the water and in any case it was never very convincing so I now just want to replace the lot and put in an access panel of my own. My big concern is ensuring that I cut a rectangular hole in the plasterboard panel without causing any damage to whatever might be behind the wall.

 

[Terry]

It looks like you have screws that are holding the panel on. That should give you access to the tank there.

This is looking inside a Geberit tank.