pfSense

It appears this is regardless of interface. WAN and floating are from the original ticket so they're used here as an example.

1. On the WAN interface, create two arbitrary rules that you can easily recognize:
- Allow any to destination 1.1.1.1, description "ONE"
- Allow any to destination 2.2.2.2, description "TWO"

2. Click the pencil icon to edit WAN rule TWO.

3. Now in a second browser tab or window go to Firewall > Rules > Floating. Click on "Add Below" and manually copy the TWO rule information into a new a floating rule with:
- (X)Quick, Interface Any, Direction In.
- click Save.

4. Now in the tab or window still with the WAN interface's TWO rule in edit mode:

- check (X) Disable this rule
- click Save

This takes you back to the WAN ruleset.

Result:
1) Now two copies of the TWO rule exist on the WAN interface: one disabled, one below it enabled.
2) Rule TWO on the WAN has vanished.

A few notes:
- Apply Changes doesn't need to be selected, and of course until it is, nothing shows up in Firewall-Generated Rulesets.txt of a status output archive.
- If you instead edit the ONE rule, then any other rule directly above isn't removed/overwritten, but it's still duplicated (see 2nd screenshot).