UML Extension Mechanisms...

[Inferjack]

Dear Modellers,

I am currently working on my own methodology which uses UML as a modeling language adopted to its needs.
UML 2.0 provides us with disciplined approach to extending language in the form of profiles. My questions are about extension process:

1. Are there any constraints on which metamodel elements I can extend? e.g. I need to extend message, metaclass which I was not able to find in the metaclasses list in EA tool during stereotype definition process.

2. I'd like to add the extra compartments to class symbol. e.g. I'd like to extend the classifier metaclass and use three instead of two compartments in the stereotype defined. How can I do that with EA?

3. I use a State Machine diagram for conversation modeling. In order to model my problem domain  
I need more sophisticated GUARD CONDITION than  
that defined in standard form. What would suits me the  
most is guard condition consisted of two parts each
including more than one boolean expression in the form
[boolexpr1.1;boolexpr1.2...][boolexpr2.1;boolexpr2.2...].
How can I do that in order to be in accordance with well-formedness rules of UML 2.0?

Many thanks in advance!

Best
Jacek

[SF_lt]

hope, OMG's UML infrastructure and superstructure documents will help you - EA provides only major UML metaclasses, but there are more of them