IMHO the idea is not so crazy as it is seen at the first sight.
Of course it will never happen with UK and other NATO members, but technically it is possible.
Look e.g. at Israel. They take MiGs as a platform only, throwing out obsolete radars and other avionics, add a weapon control system with interfaces to non-Russian missiles and sell worldwide.
And in this case the issue of malicious lines in the source code can be eliminated.