Addition Of Co-applicant In Sales Deed

I am due to register my property where I want to add co-applicant in sales deed however had availed a home loan with a single applicant. I would like to know whether I will request my builder to incorporate the co-applicant in sales deed and submit to Housing finance company or I have to give request to both parties (i.e. builder and HFC) as I do not want to change in EMI pattern which is with the primary applicant.