First of all, the fork should fit your frame. The question you have to ask is, "Is this fork appropriate for my bike?". The answer to that is, "No".

The reason, your frame was designed to work within a small range of travel for the suspension fork. Moving outside that range will greatly affect the geometry of your bike. You may or may not like it. However, it CAN be done.

Also realize that your frame was not designed to withstand the forces applied to the headtube/top tube/bottom tube intersection and this may become a point of failure of the frame.

However, a free fork is a free fork. I wouldn't advise it, but go ahead if you want.

I will add that I've seen a lot of people put triple clamp fork on bikes not designed for them and have ridden them for years without incident. I've also seen frames fail in 1 month of riding.

Your other question regarding converting a standard hub to a 20mm through axle. Can't be done, you need a new hub/wheel with a 20mm hub.

There are some hubs that have converters to allow a 20mm hub to be used as a standard hub, but not the other way around.

L8R