Code to boot into PAL or NTSC modes?

[psxphill]

There is more to it than that.

It's generally all that anyone does though.
 
http://thecryptmag.com/Online/49/PaltoNTSCandBack.html
 
You can update execbase too, the source code here does that.
 
http://aminet.net/util/misc/60HzEmulator.lha
 
A lot of the source is useless, it allows switching using key combinations and faking vblank using a cia (if you don't have a fat agnus).
Updating exec base is mostly useless, generally the reason why you are switching is because the software doesn't bother to detect the mode.

[psxphill]

Else all the Amigas blitting routines and so forth would have wrong clip limits, wrong overscan limits, etc. Nothing will work right.

Setting the refresh rate doesn't change how much chip ram has been allocated for the screen, so blitting would never be affected.
 
I'm pretty sure that it just leaves a blank area or clips the screen, depending on whether you're going from NTSC to PAL or PAL to NTSC.
 
Most games never look at execbase, they just open the screen they want (and usually with custom copper lists). Running a PAL game on an NTSC Amiga just crops the bottom off.

[psxphill]

Are you claiming that all games do not use MrgCop()? Or any other routine in the kickstart ROM whatsoever?

Most games don't, they disable multitasking, use custom copper lists etc.
 
WHDLOAD has to do it's magic to run them from hard disk.

[psxphill]

A super simple one might work ok for a few games but all the rest will be braindamaged.

A super simple one will work for the majority of 80's/90's PAL games. The later HD installable ones tended to be more system friendly, but then they would generally open the screen mode properly anyway.