Yes, it is possible, I have done it.
You have to create your own utility class to process you annotations.
Normally, only one utility class is included in the generation process:
<property key="hibernatetool.util.toolclass" value="org.jboss.seam.tool.Util" />
you can add your custom one like this:
<property key="hibernatetool.myextension.toolclass" value="domain.mycompany.MyUtilClass" />
After that is only a matter of using reflection inside your utility class to process your custom annotations (and of course calling your utility class from your custom freemarker (ftl) templates).
Take a look at seam-gen ant scripts look for the place where the hibernate task is called.
Thanks for your reply.
A little bit more could be helpful.
I Know to analyse existing annotations with an own utility.
I know to modify
I know to set
I don't know to place my own utility inside of editproperty.xhtml.ftl and which arguments are possible for my utility.
I fear that i have to analyse seam-gen from scratch.