How to disable Blanket Purchase Agreement from Style LOV in Create Agreement task?

Summary:

We only use Contract Purchase Agreements and no other type of agreements. Our requirement is that when Create Agreement is used, then the Style field should have value Contract Purchase Agreement by default. Other values should not come up.

In Manage Document Styles setup, we have been able to change status to Inactive for all other seeded styles except Standard Style. Using this, all other values in the LOV for Style in Create Agreement are no longer coming up except BPA and CPA. For Standard Style, we need to just disable Blanket Purchase Agreement but the Enabled field is greyed out and we are not able to disable it.