>Leaving aside the fact, that whole complicated code is already written based on ALTER TABLE, how can I do this process for DBC's tables?

How about using something similar to this:

use MyTable
copy structure to TempAlterTable
alter table ... && as usual, but alter table TempAlterTable instead of MyTable
use MyTable
zap
append from TempAlterTable

You would have to include a few more commands, of course; for instance, perhaps you might prefer to use sys(2015) instead of TempAlterTable.

HTH, Hilmar.