I’m assuming this is a two part question.

If you’re asking to change the wording of the clause beyond what we are allowed to put in the two inserts, that must be done through the FAR Council.

For the preliminary written notice, “at least” must be used.  It is actually the better choice.  If you change it to “within”, then you can only provide the written notice within the time period you specified in the clause, and not earlier.  By keeping “at least”, you can provide notice to the contractor of your intent to exercise the option 60, 90, or even 120 days before the option expires.