The Apple Pencil Scribble feature can rename all labels that offer a Rename option, including:
Save file dialogs
Renaming subtools
1.) Double-tap a Subtools label with pencil.
2.) Double-tap the text to select all.
3.) Scribble a new label to replace the selected text.
4.) Tap the Enter key on your iPadOS virtual keyboard or standard keyboard.
When applying scribble to a file you're about to save, scribble can be applied with the above steps.
If the Enter key is not pressed while text is highlighted, the scribble label reverts back to the previously assigned subtool label.