How can we improve WHMCS?

Hi, as we know currently whmcs set invoice generation to all client, but cannot per client/group.
For example default to all client is 14 days before due date to make invoice generation, but we need to setup for some client only to set 1 month before due date.

So i hope in the future whmcs have feature to set automatic invoice generation for some client/group.

Thank you very much.