We can inference lock using the SHIFT key when drawing or transforming objects.
I'd like to suggest that this locking be taken another step forward by adding the ability to lock the values of the Input Palette.
This could be done by a shortcut key .... ALT + TAB. That keyboard shortcut is not being used for anything in the Load Defaults ... button of the Key Shortcuts Manager.
Unfortunately SHIFT + TAB was already taken by "Pick Parade - Previous" which actually works on the Input Palette to TAB backwards to the previous edit value box.
Shift + TAB or TAB could be used to "Unlock" the value if needed.