Writing a large part of a grant as a postdoc
Appointments to more permanent positions (like tenure-track or research faculty) are typically made by the university, not by receiving a grant. In other words, I cannot pay myself more simply because I received a grant with available funds. Depending on the university rules, postdocs may not be eligible to be a project PI, which may limit your ability to submit those ideas as your own grant proposal.
In some fields, it is common for postdocs and even PhD students to write grant proposals for their PI as training for their later career. That could even be part of the job expectations for a postdoc. Although you may not have much leverage to receive more funding from this grant, having written a successful grant proposal is a good experience that should help you succeed as a tenure-track faculty and possibly in the job market as well.