Can I negotiate the price with the Housing Association if I am buying 100% of a Shared Ownership offered flat?

I have seen a flat that can be bought 'Shared Ownership' or bought completely out right.
I have heard that you cannot negotiate on price when buying Shared Ownership and I was wondering if this is only if you are buying a share.

If I can negotiate on price, I would maybe buy it in full.
I would like to potentially 'Let' this flat out while it is still on the mortgage. Would this be possible or do I need a special mortgage?

As you can tell, I am new to this. I am a first time buyer. I have so many questions. I cant decide whether to buy 50% and save a little money or 100% and know I can Let it if I want. Or maybe I couldnt. Aghhhhhhhh!

Thoughts on buying from Housing Association and mortgages that let you Let please.
Any advice is welcome.

Read more: Can I negotiate the price with the Housing Association if I am buying 100% of a Shared Ownership offered flat?