Hi Prasanna,
I grappled with this for a long time a few years ago since I had to update reservations while in an exit within order save. And since I was extending existing code I did not have the option of writing code outside this enhancement. After trying to use MB_CHANGE_RESERVATION unsuccessfully I found a usage pattern in SAP code to update the RESB table.
Note - this required a lot of testing to ensure all entries were correctly updated in the DB.
The sequence of FM calls to update memory variables for reservations was:
1. CO_BT_RESB_SET - Call this providing order number
The following in a DO...ENDDO. loop.
2. CO_BT_RESB_GET - Call this to retrieve a single row of RESB entries for the order
(Exit loop on exception eof)
3. Modify the retrieved RESB workarea as required
4. Finally call CO_BT_RESB_UPDATE providing updated WA from step 3 and index of current loop.
That should do it.
Cheers,
Ash