LMN & Co, an unregistered supplier under GST wants to claim input tax credit and collect tax. Can it do

Dear

Without taking registration in GST , You ,neither take credit of GST nor Collect the GST by the way of issuing invoice.

Further to collect GST from Customers and to take credit of GST, you need to register as REGULAR Tax Payer in GST. 

To claim input first you have to get registered GST.

Either I did not understand your question or you have not asked it properly.

To claim input tax credit first register under GST and after registration you can claim input credit on your inward supplies.