Pilot-DB is distributed under the GPL licence; it is mandatory to redistribute Pilot-DB under the terms of this licence and thus be able to supply source code even if you have modified it.
If you are not aware of how to distribute your modifications, or if you want to benefit from the main branch of Pilot-DB feel free to contact us contacter.
You are not restricted in any way from distributing your databases. The Pilot-DB web site can help you to distribute them provided they are offered free of charge.
It is possible to close a database somewhat to users. If this interests you, contact us.