how does this work?

Hey everyone just a question I cant get my head around here.
Say I have 10,000 shares and I accept the offer for 3750 shares and have 6250 shares left over.
Can I sell these shares before the offer ends and reduce my holding without compromising the shares I have already accepted the offer for.
If my holding reduces before the offer period ends will my shares they want to buy reduce also?
Also how do people know the shares im selling have no right to the offer?
Or is there one record date for you to be eligible for the offer.
Sorry to be confusing but any help on the subject would be great.
Regards Newy