Field behavior...

[GS]

how to change it on the fly or via script?

[bcooney]

Field behavior is not scriptable.

If you tell us what you're trying to achieve, there may be other techniques you can use.

[GS]

I would like my fields to be locked when browsing records, then allow entry when a button 'edit' is clicked. What I have in mind is to switch to identical layout with allow-entry permission upon clicking 'edit' button then use 'OnObjectSave' trigger script to switch back to original layout. Do you have a better solution?

[bcooney]

That sounds good, and is what I often do. However, I'd use Record Commit, or a Done button that switches back to locked layout.

Also, check out Security and Privilege Sets with Record Level Access rules to "really" lock out editing of fields.

You could also simply have a button set a flag = 1, and define the RLA rule to allow edit if that flag=1.