<<I am about to buy a 15-1994 remote and have some questions. When recording a macro, can you jump between different device's, or must the recording occur only within one device?>>
A macro is just a collection of keystrokes, so you can include the device keys, no problem. In fact, as macros in the 15-1994 are global (in other words they will be in effect in all device modes) it's a good idea to make the first button the correct device key.
<<After recording a particular button sequence, can one of the buttons in the sequence later be reassigned a different code without altering the original macro?>>
No.
<<My TV, DVD, and AMP take a couple of moments to power up before they can receive any additional commands. Is this a problem, or can the sequence be slowed down enough to get the entire macro to work?>>
With a bit of cleverness, you can make it work. You could poer up the tv, then the DVD, then the amp, then come back and put the TV in the right input mode, then switch to the DVD and/or amp, the time it takes to power up the dvd and amp might just be enough for the TV to get ready. If that's still not enough delay time, you could include a "dummy" button in the mix to slow things down. There's more details on how to do this in the FAQ on my site.
<<Will changing the batteries erase all of the macros?>>
All settings are written to non-volatile memory, so they will survive removing the batteries.
Rob.
http://www.hifi-remote.com