Hi,
As far I have seen, it is a manual process via cutovers. We add those TRs to Maint DEV system manually and repackage them so as to reduce the number of TRs. Then the normal charm procedure is followed in Maint landscape to move them to PRD. In some blogs I also read about adding these TRs to import buffer of all Maint. systems (DEV, QAS, PRD) and importing them directly (not through charm). However I am not very sure about the latter method.
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Regards,
Vivek