It is not possible to use a Dataclas defined in the ACDS if the ACS code does not assign it.
In most companies the ACS code will check it is a valid Dataclas and just accept the one you have coded in the JCL.
However they may also have code that will check the Dataclas you've coded and then also check some other variables like USERID and dataset name for example and decide you can't use that particular Dataclas. They may just assign another such as a DEFAULT one or just exit and abend the allocation.
These decisions are entirely dependent on your particular companies ACS code policy, so you have to ask your Storage people what applies.