Plastering fix help

[Wolf359]

Removing embossed wall paper to paint underneath the walls has uncovered some pretty crappy plastering work. When the extension was put on, the ceiling plaster must’ve smeared excess plaster onto the tops of the walls as there are places where a fine skim continues down the walls and ends abruptly. Another cowboy job we have uncovered.
We cannot afford a plasterer to fix this, and plan on reworking the whole extension in 3-5 years anyway. So I need ideas for the best way to rectify it without spending much. The plaster smear areas will chip off to reveal acceptable plaster underneath, but the it has some sort of string matting which is attached to the ceiling plaster. Can this be cut with a Stanley knife around the edge? Photo to follow

The green part is the overlap of plaster. Pink plaster is the rest of the wall. It is like this all along one wall.

You could cut the plastering mesh with a Stanley knife, but I wonder whether you'll find it's been used to help fill gaps between the top of the walls and the ceiling; we uncovered quite a few horrors like that.
Good luck!

Thank you, will give it a go and hope there are no horrors waiting underneath