I don't known if is it possible or not, if there are present security reason (isolation) or not, but i think could be don't much difficut obtain what you want (integrate all your projects) on one big projects if you follow some conventions.
For the moment i don't development using seam (before i have some questions) but when i see some example as jboss-seam-jpa on seam i see that even using different projects:
the web.xml remain the same;
the faces-config.xml remain the same;
the components.xml i don't known if remain the same of your must doing some changes;
on the pages.xml should be sufficient put each projects on a sub-directory;
on each projects, if they use different template,should be necessary rename the template so change even the name of the template on each xhtml involved;
add a layer where you make a choice of the project that you want use or eventually, if the access on each projects use a different login/password, the user don't should choice anything.
Sure there are some code to add on the projects but i don't think is too much.
Furthermore, as a secondary effect of these changes, if you should sell only some projects (despite i don't think is your case), will be sufficient only some change on the configurations and remove the project unnecessary without touch the code, for develop a custom war for some clients).
However please remember that i don't known well Seam, but given the
levels of decoupling
present using these type of frameworks, theoretically these changes should not be too traumatic.
Some general discussion about multiple repositories sharing a single JPA:
Multiple repositories sharing a single JPA Source