Replace matching brackets

A trick from StackOverflow.

Example:

%r]^or[.

Explanation:

• f( -- put cursor on first parenthesis you want to change (if it's not already there).
• % -- jump to the matching parenthesis.
• r] -- replace the parenthesis with a bracket.
• CTRL-O -- jump back to to first parenthesis.
• r[ -- replace the parenthesis with a bracket.