Editing Squash commit message in merge request when "Fast-forward merge" option enabled

Hi Everyone,

For our workflow, we want the merges from development branches to our mainline branches to go in as a single commit (squashed with no additional merge commit). We have configured the merge method to be “Fast-forward merge”. However, we would also like the ability to modify the squash commit message in the merge request. This option “Modify commit messages” is shown when the merge method is “Merge commit with semi-linear history” but not when it is set to “Fast-forward merge”. Is there a reason for this? Is there any way I can enable this option when configured for fast-forward merges?