Quoting a discussion on fedora-devel:

rpmdev-bumpspec -c "Change here"
fedpkg commit -c -p
fedpkg build

One way to to do this with rpmautospec is:

git commit --allow-empty -m 'Change here'
fedpkg push
fedpkg build

But it'd be nice for fedpkg so support this natively so calling git is not necessary:

fedpkg commit -m 'Change here' -p
fedpkg build

Right now this fails with Could not execute commit: Failed to execute command.
The error message is also not very helpful.