I have released two updates for RIn.Rename. Version 1.7 brings faster ways to switch and type names, and 1.8 focuses on renaming bones in symmetric rigs.

• Add Side: type a bone name without a side, eg. arm01, and each bone gets the side it’s on: arm01.L, arm01.R. The side keeps the old name’s style, or follows the new Default Side Style preference (.L / .R, _L / _R, _l / _r, .l / .r or a Left / Right prefix).
• Symmetric Numbering: with bones on both sides selected, each side is numbered on its own, so you get arm01.L, arm02.L, arm01.R, arm02.R whatever order you selected them in.
• Mirror Bone Renames: rename one side and the other side follows, vertex groups included. Mirror bones are found by name, or by position when the names don’t match.
• Bones selected together are numbered along the chain, from parent to child.
• Bone fixes: name clash warnings, /ib and /eb in Edit Mode, = with bones selected, and Single Selection Mode renaming the wrong bone.

• Switch Words: type /s for buttons that switch _high / _low / _cage or _L / _R in the selected names, or swap them.
• Aliases: 9 short triggers that expand while you type, eg. hand.l → hand_left.
• Outliner hotkeys for favourites: give a favourite its own hotkey and rename the Outliner selection with one key.
• Names in any language: words, separators and case commands understand letters of every script (eg. テスト, café).
• Only the last typed number counts up, eg. Car22__01 → Car22__01, Car22__02, ...
• Swapping names within the selection (eg. Arm_L ↔ Arm_R) no longer adds .001, plus many more fixes.

See the full list in the changelog: 1.8.0 and 1.7.0.