There are 4 modes for macros available. One of those supports running a macro in a loop as long as the key is pressed, but there is no on/off. Macros are already a grey zone in gaming, therefore I decided not go for such an on/off function. Nevertheless, if you want to go for such a functionality, you can do this easy and very cheap with less then 30 lines of code with another micro controller that support HDI protocol. Basic code you could find on Arduino or on Google. Hope this may help.

I'll will put this to the feature list. To ensure that usage of macros is not easy detected by games there is a internal random deviation of +- 5 ms by default.