Owner financing extending a balloon question

[Robert L.]

I've got an owner financing agreement with a 5 year balloon but I wanted to put in verbiage to have an optional extension for 3-years per buyer's discretion? 

Is this something that I can put in the 'additional instructions' section of the contract?  I didn't want to be locked into a 5-year balloon in case I am unable to refinance, etc.

I know I should consult with an attorney, etc. but was just asking for an opinion.

Thanks!

Rob