Line main halyard ?

You'll have to replace the ball with a halyard hook, link below
http://www.murrays.com/mm5/merchant.mvc?Screen=PROD&Store_Code=MS&Product_Code=56-6812

And on the halyard, install a ring
http://www.murrays.com/mm5/merchant.mvc?Screen=PROD&Store_Code=MS&Product_Code=01-4216

I'm ALL about AMSTEEL, personally. My halyards on both my Square and my trimaran are Amsteel.

I replaced my jib halyard on my 5.2 with dyneema. It made it so light that if I forget and let go of the halyard after detaching the jib, the weight of the block on the end will cause the halyard to run itself all the way up the mast. There are quite a few people who could chime in as to how sick of flipping my boat over to retrieve the halyard they are.

I just bring that up to point out that making little (or big) mods is never as simple as it seems.

Yurdle
perhaps contemplate running the halyard thru the center of one of your horn cleats and stopper-knot the bitter end.

It goes the other way..

The halyard shackle runs up to the block on the mast. I've learned to wrap it around my hand or finger a few times before I unhook it, and I no longer have issues with it, but it took me at least a month of sailing with it before I could remember to do that every time. I'm sure all day in the sun with boats and beers wasn't good for my focus.

Not sure what dia your boat came with orig, but I went down in size on my boats to 3/16. Prob stronger than original thicker line and much easier (less friction) to raise. I use New England Rope Sta Set