Addition of new partner and change in profit sharing ration

New LLP Agreement need to be incorporated and to be field with LLP-3 Form and the same stamp duty need to be paid in form of stamp paper s it was paid at time of original agreement.

You can execute Supplement Deed / Deed of Accession for altering clause for Profit Sharing. The stamp duty will be minimum (in Maharashtra, we are paying Rs 500 on Supplement Deed) since you are not increasing the capital of LLP and you have already paid stamp duty on original agreement.