Yes, static users can be edited if a pushpage is schedule to send

When trying to edit the distribution group that is tied to a scheduled pushpage, you will see a message stating:
"There is at least one scheduled, running or paused job associated to this Distribution Group. Changes to this Distribution Group will affect scheduled jobs. Changes to this Distribution Group will not affect running or paused jobs." 

Therefore, you can edit the static users in a scheduled pushpage so that the pushpage will only send to the new, updated static users. If the job is running or paused, these updates will not take and it will send to the old static users.