Is it fine if I use this thing cuz the rule don't say any thing about it it's not an engine I used bp edit bc it's allowed and it didn't say any thing about this I don't expect this to be allowed
It is not allowed indeed. We accept bp editing, but the spirit of the rule is that it must not give an unfair advantage.
All bp editions made for cosmetic purposes or for accurate design pose no problem. Editing the size of a fuel tank is fine for example. You get more fuel, but the tank is also made heavier in the same proportions. In the end you could just achieve the same result by combining several smaller fuel tanks, so it's ok.
Streching an engine is forbidden however. This is because when you strech it by a factor 2, you get twice the thrust, twice the fuel consumption, but the mass remains the same. Now you get an unfair advantage compared to a pair of unstreched engines.
The same goes for editing the separation force of a separator. In this case this would give you a free and powerful kick that is not acceptable.