Cutting walls 11.5 / Alternatives

I broke open the plaster today. It is about 1.5 cm thick. I asked around and the opinions are always along the lines of: that has been there for ages, what could happen / be careful when slotting both sides / my brother-in-law did it the same way / it will be plastered over again...

I will now wait to see what the electrician says. Unfortunately, he is on vacation until Tuesday.

The old empty conduits already embedded in the masonry are unfortunately too thin for NYM and network cables.

Can you remove empty conduits? If yes, you should have a fairly large groove open. Regarding NYM and network, distances must be maintained.

Yes, I should be able to get them out of there. They are about 2cm under the plaster.