You can place a macro on most of the hard keys as well as any LCD key on the MX-450. It is best to use a hard key that is not needed or not used for a particular device.

If you create an instant or non delayed macro for a hard key it will override the programmed function of the key. However, if you create a delayed macro it will execute both the programmed key function as well as the delayed macro if you hold the button for the prescribed delay.

If you don't need the programmed function of the key chosen for the macro, you can override it with a dummy learned command since learned commands always override programmed commands. For example, you can get a DVR or VCR command from another remote for use on the HDTV device mode on the MX-450. The learned command will override the programmed command and do nothing on its own before the macro is executed.

I use such a setup for the record key on my DVR device. I do not want to accidentally press the record button so I entered a dummy learned command to override the programmed record command and placed a one second delay macro on it referring to the actual record button on a hidden page. I must now hold the button if I want to actually record something.

I assume that all of the above will also work on the R40 & MX-780.