How fungible are personnel salary allocations in an NIH grant? I'm preparing an R01 for the NIH in which I allocate salary to myself (the PI) and two co-Is, as well as to non-key personnel including a postdoc. However, in actual practice, I think there is a good chance that I'll prefer to do myself the work that might have been allocated to a postdoc (e.g., if I prefer not to hire a postdoc because I don't find the right match).
If the grant is funded, would I be allowed to simply reallocate salary from the postdoc to myself (with a reduction in FTE)?
Generally I think yes, but definitely talk with your institution/department's grant staff about this even if you're still in the writing phase - they'll be your best friends.
For example (from NIAID but I don't think this is Institute-specific):
https://www.niaid.nih.gov/grants-contracts/putting-effort-your-application

Don't worry if your effort changes over the course of your grant. Reviewers know that can happen, and NIAID allows you to change your effort as your work progresses (with some limitations we'll discuss in a future issue).

One of the exceptions is substantial reductions in effort for key personnel:
https://grants.nih.gov/grants/policy/nihgps/html5/section_8/8.1.2_prior_approval_requirements.htm

A significant change in the status including but not limited to withdrawal from the project; absence for any continuous period of 3 months or more; reduction of the level of effort devoted to project by 25 percent or more from what was approved in the initial competing year award.

You'll have some opportunity to firm up the budget if your award is funded and during the extensions process.