Text frames have fixed dimensions, which can only be changed manually. InDesign has auto-resize options that will adapt to the content, but FrameMaker does not.
Note that if you end up overriding the template frame size on a body page to accommodate your workflow, and then later make an edit on a master pages, when you return to the body pages Fm will alert you to an override. Say yes to keep your custom frame sizes. Generally speaking, overrides of any sort are not a great idea when you are managing long documents.
Sharing screenshots and a more detailed description of your workflow may allow us to come up with a better solution to your needs.