Purchased the Spheres of Might PDF and Hero Lab files off of Drive Thru, is there a way to create custom martial traditions? Or am I stuck with the provided ones?

The Highlander's Handbook is not currently on the development schedule, so your best bet for now is to use the editor to implement it yourself. I would recommend taking a look at how some existing SoM archetypes (such as the Berserker) work to get an idea of how to create an archetype that uses the spheres systems.

Yes, creating your own martial traditions is supported in the editor (I try to make as much Spheres stuff editor-accessible as I can). There's a subtab for it under the Spheres of Might tab.

Is there any intention of coding in the Mythic Spheres books? I LOVE the spheres but I don't have the patience to manually write everything out once my group goes Mythic.

Right now we're focused on getting Ultimate SoP done. No plans beyond that have been made yet.

Our group is mythic, and I've given the players seven books (including the sphere options) to choose from.

I basically have the source book and page, then the power name.
So at least it's relatively easy to reference.

It would be awesome to have within HL at some point.
Really looking forward to USoP.

You can also use the Adjust Tab.

Search for Spheres of Might, in the top box to get all the Might adjustments.
Change the Martial Traditions allowed (to zero) by adding that adjustment and giving it a -1 value.
Then add Talents known or Talents allowed, it's something like that, and set the value to +4.

A tradition is basically four preconfigured talents, usually one from Equipment and then following some kind of theme.
You could experiment with more or fewer talents.

This approach is manual, as you'd have to do it each time.
But you could easily make almost any type of tradition, without messing around with the editor.

So what exactly is the situation with SoP and USoP. if I buy the current files are they partially updated to USoP based on what I read in the 1st post or what?

SoP and USoP will be separate data packages/files. The second is not an update to the first. USoP is currently being worked on.

This isn't quite accurate. USoP will effectively function as an update for anyone who installs it over an existing set of legacy (i.e "regular" SoP) files. I'm keeping the filenames and thingid's the same as much as possible, in order to minimize the amount of work a user has to do to update a legacy SoP character to USoP. I'm afraid I just don't have the resources to make a version of USoP that can peacefully coexist with legacy and let users pick and choose elements from each for their portfolios, much as I'd like that.

How far along are the HL files for USoP?