you can use one of the free registry editors (total commander or registry editor), just search for it, or use this mobile registry editor and run it from your pc.
you can then use the registry editor to edit the file for landscape like so (write down before you change the registry in case you need to go back):
[HKEY_CURRENT_USER\Software\HTC\Manila]
"EnableLandscape"="true"
"EnableFullScreen"=dword:00000000
[HKEY_LOCAL_MACHINE\System\GDI\Rotation]
"LandscapeMode"=dword:00000001
[HKEY_CURRENT_USER\Software\HTC\HTCSENSOR\GSensor]
"AutoRotation"=dword:00000001
[HKEY_CURRENT_USER\Software\HTC\HTCSENSOR\GSensor\WhiteList]
"SENSE"="Manila"
[HKEY_CURRENT_USER\Software\HTC\HTCSENSOR\GSensor\ModuleName]
"SENSE"="\Windows\manila.exe"
This is where I got the registry from, but I just left the last line out since that doesn't apply to this rom
http://xdaforums.com/showthread.php?t=712471&page=2
(ps if the line is not there then right click and add it in, if it is a word then use string value and if it's a number then use binary or integer value depending on what editor you choose, I use the mobile registry editor myself) It's that simple.
I'm not sure what power key you're referring to and I didn't use the shortcut keys for preinstallation so not sure. Hope that helps a little, of course, ultrashot may give more light on all this for you. Enjoy my friend.