I've never had any problem with reallocation/merging, i.e. taking the credit line from an account I'm about to close and adding it to another before closing it. This is with Citi and Chase (not Chairman cards).

I don't think there's anything "taboo" about this... I think most issuers explicitly allow it for customers in good standing (Amex even lets you do it on their website). Not sure why this needs to be kept hush-hush?