License re-activation if contract expired - what happens?

Hello,

i took over operations of a F5 LTM unit and currently plan to upgrade it. I'd like to upgrade it to a newer software release (security concerns) and have problems understanding the licensing, specially re-activation. The unit was covered by a contract untill 2017-11-13. However the service check date is well before that (2015-12-16). Now to upgrade to 13.1 i need a service check date of 2017-09-12. To get this i have to re-activate the license, if i understand correctly. So my questions is, what happens if i try to re-active now? Will this work and set the service check date to 2017-11-13 (when the contract expired) or will there be any problem? If i got it right, this process will also briefly interrupt traffic?

Thanks, Jonas