Hi Merve,
Sorry for late reply. Don't know if you figure out by yourself but anyway, here's my thoughts.
When I've used this I was working mostly with IC business roles, maybe this doesn't work so well with ITSM business roles.
This way, and since I suppose you've enhanced BT_APPROVAL, you can create there a public static attribute there for process type. Then, for example, in DO_PREPARE_OUTPUT method, just fill this attribute with the value of current business transaction proccess type (use context node BTADMINH to get that).
With this, you'll be able to consult this value from your user-exit function module, as long you're using WebUI.
Kind regards,
Garcia