The only way your probation can be extended is if you sign, agreeing to extend your probation. If you refuse and the probation officer feels that there is a basis for revocation, the officer can send your file to court to request that the judge and CLO (court liasion officer - probation officer) review the file and consider a revocation. The judge can order you come in for a little talk or can issue a warrant and have your brought in. Then the judge can decide how to proceed. It really, really depends on the judge (and there are 15 county court judges in Harris County - with different ways to handle matters.)
Short answer is no unless you agree to it. Only the Court can unilaterally modify probation terms and conditions. That said, if the PO wants to extend you and you don't agree they could refer the matter to the court for guidance on how to proceed. If you have not given them reason to order this new condition and modification the court might see it as overreaching by the PO but some courts look to the PO and will do what they request.
Consider your options extremely objectively. You don't want to get revoked so determine if the 3 months is a good idea or if your PO is just being difficult before proceeding.
Good luck to you.
The judge has the ultimate say, but obviously in many courts, the probation officer has a lot of power. You need to involve an attorney who can contact the DA and bring them into the discussion. The DA will often calm down an overzealous probation officer when the DA is forced into having a contested hearing on issues like this.
You can't be extended with your permission because that would be a violation of your plea agreement.
My answers are only intended as general legal advice based on my eighteen years as an Austin criminal defense and DUI attorney. They are not intended to be a binding legal opinion nor to create an attorney - client relationship. For those questions asked outside of Texas, there is no intent on my part to practice law in any other state There is no substitute for contacting a local attorney. Feel free to visit my website, www.austincriminaldenseattorney.com .