I can confirm this - the abiltity to edit (and disable) custom field options was added around version 4.3 (my memory isn't great - I know it was NOT in 4.2, and it was definitely in 5.0, I'm just hazy about 4.3 or 4.4)
Version 3 of Jira simply does not have any edit facility. The only way to do it is with massive risky SQL hacking.
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