HSN /SAC..registration amendment needed??

Hi guyz,

please solve my query below.

A person is registered with GSTN as "service provider" means he had included SAC code only while applying for gst registration.

Now he want to trade in goods also for which HSN is not entered while
applying for registration.

question:
1) can he trade in goods without amendment in gst non core details??

2) what if he has already purchased and issued invoice of goods, if he has not amended his GST registration. in this case, any timelimit??