Under - 10 season ticket

I'm considering geting a season ticket for my four year old son and, due to the low cost for an under 10.

However, it is unlikely that I would take him to every game in the season such as some evening games because of his age.

Is there anyway at all that for the games he does not attend, I can let another adult use the ticket and pay the difference ot take someone else to fill the seat?

Yes, you could pay the difference and exchange for an adult ticket.