Deactivate NewGL on S4 HANA 1809

Dear reader,

I'd like to know either it would be possible to migrate on a S4H 1809 version without activation of the newGL (tcode: FAGL_ACTIVATION).

My customer would like to spare some times by doing a kind of step by step approach.

I know it would be easier to migrate and activate the NewGL functionnalities but right now i need to know the technical feasability of the system.

Thank you very much.