With MTA UI engine and NFSSA GUI library it's impossible to do this - it would require to rewrite half of server scrits.
Minimum supported and requried resolution for NFS:SA is 1024x768
If your GPU doesn't allow to set higher resolution (even with 800x600 display) it also means that your general PC configuration is way too weak to play NFS:SA which is the most demanding server in MTA.
Also, in 2018 nobody shouldn't think about such old and low resolution anymore.
Minimum supported and requried resolution for NFS:SA is 1024x768
If your GPU doesn't allow to set higher resolution (even with 800x600 display) it also means that your general PC configuration is way too weak to play NFS:SA which is the most demanding server in MTA.
Also, in 2018 nobody shouldn't think about such old and low resolution anymore.