Can i limit the lot size opened on my MT4 when it receives signal from an mql5 signal provider
if lot my platform wants to open is 1.0, can i use EA to modify this lower
Yes, you can and there are EAs and utilities in the market that can do that.
please is there a topic on this in documentation, codebase or an article on it
am looking to learn it
I don't know of any documentation.
Lot size modifiers in general are highly unadvisable, when it comes to signal copying, since they mess with the money management signal provider had in mind.
You can always use less than the 95% max in your account's participation percentage in: Tools, Options, Signals settings of your MT platform and decrease the lot size copied in your account.
As I wrote above, there are some EAs and utilities in the Market that can do that also.