Hans, It's possible to remap anything to anything, but customizable remapping would be slower than hardcoded ones like used now. If you want to learn how to write such things yourself i recommend studying C, Assembler, WinApi and DirectX.
ScrollLock is keyboard state, so it has no relation to what you do within RO, it was made this way to affect all running RO clients simultaneously. Ctrl+S is RO instance state that starts as 'off' when you start RO (you can easily see it's on by reduced in-game fps).
Zone, RoExt definitely can make RO use less resources or has no effect at all, but i never saw a situation when it makes RO lag more than clean client.