It will likely conflict most in-progress PR. For PRs that are large and long lived it will be a PITA to maintain and will further slow integration so, likely, yes.
I ran formatters on a largish codebase over Christmas when all the PRs were done. You just have to pick your moment. If it's really hard then get everyone to agree on a date to do it and make it each developer's responsibility to either merge before or rebase after the change. It can be done.
