[Dragokas]

No, I didn't resolve it in the normal way.

The mentioned way is ethically a bad idea from L4D devs. Because now others' people servers conflict with that manifest file if they may also want to use his own custom manifest for that particular map, but they can't do it anymore due to overwriting protection.

The only good way to use it if you are the author of a custom map.

I would also recommend you to incapsulate manifest in a vpk addon file, making less troubles for people to resolve conflicts similar to described one. You are able to use it with FastDL.