Process of transferring excisable goods to other unit.

Hello everyone! Wish you all a very happy new year ahead.

My question is what is the process for transferring excisable goods to another manufacturing unit of same concern when-

(a) ssuch excisable goods is transferred while in transit; and,

(b) excisable goods is already received in the factory of unit originally buying the goods.

Please note that the invoice is in the name of transferring Unit and Cenvat needs to be claimed on the goods transferred.

For example, suppose A has bought excisable goods from X. Invoice has been issued in the name of A. Goods has been transferred to B by A. Now the question is what should be the lawful process for such transfer so that Cenvat is not lost and no provision or rule is voilated. Please suggest in following two conditions-

(a) such excisable goods is transferred while in transit; and,

(b) excisable goods is already received in the factory by A.

Would appreciate a precise and to the point suggestion/ discussion.