Hi George,
Thanks for reaching out! At the moment, we aren’t able to fulfill requests for adding custom numbers of activation slots to a single license key. I’m sorry to disappoint! If you only wish to add ten Events Calendar PRO activation slots to your account, rather than upgrading to our Unlimited tier, I’d suggest purchasing a new Events Calendar PRO license key at the Agency level. You may then distribute your two license keys across your network of sites in any way you’d like–and, of course, you’ll still have the option of moving to Unlimited later, should you change your mind. 🙂
I hope that helps! Thanks again, and let us know if you should have any other questions!