use rather the descriptor file to set it (as you did).
it may be also helpfull to reset the portal instances tables in the database.
so you make sure you are using the exact new definition (sometime it may mess with the definition from the manager and the one from the file).
look at posts about reseting the portal database, to clear the instance definition (becarefull, you will loose all the changes that are not in the descriptor file).
if this is the pb.
if not : I don't see why.
these things you want to do works perfectly.
may be a small detail that goes wrong in what you have done (you know, bugs we don't see until they appear "so simple").
I am also using jboss-portal 2.6 beta1 and facing the same issue.
Has anyone got a solution?
Is this a bug?
Mohan were u able to figure out any solution for this?
Yes, the update button is missing in beta-1 i use cr2 .
But cr2 is having some problem with IPC (inter portlet communication).