I am using a bar which can be switched from top to bottom. It already resizes the DesktopArea so that maximized windows will not disappear behind the bar. Is it possible to resize / move the existing windows on switching, because otherwise maximized windows when at bottom cannot be accessed at top mode.

It's possible to move/resize almost whatever you like, and when you like. But I don't clearly understand what you really want to do.
If you use jDesk, maximized windows are always rezise on desktoparea change

You need to unmaximize them and then maximize them again. I don't know if there are any bang commands to help with that... (anyone know? and on a related note, is there anything that will let you restore/max/minimize/move windows identified by handle?)

It's more difficult if you have maximized windows on other virtual desktops, because they'll try to come to the current desktop. Maybe set a flag and remaximize them when you switch to that desktop.

Say the bar has a height of 40px, then all windows should be moved 40px down if I switch from bottom to top mode. It is not only important to maximized windows, because other windows could also be overlapped by the bar.

As I said, jDesk resize automatically maximized windows on desktoparea change.
For other windows, there's modules that can help you (RabidVWM for windows class/title/handle detection, WinPlace for moving/resizing and WndMan) but I don't know if there's a real good solution; and I think you're loosing your time(hope I'm wrong).
Good luck

Ah, I see. Maybe get WndMan and use...except that doesn't seem to do anything :(

maybe just minimize em and then restore again :)

btw you have to have the latest ils (9.02.2003) because in some earlier versions those minimizing-restoring things didn't work ;)

Thanks. I just tried jDesk and it does exactly what I want.
I use