Modify Soma 1/2 iron training plan?

My plan is to keep two of the swims a week and drop the 3rd when it's on the plan and add an extra run per week to my schedule. 

I would replace some of the swims with bike rides. You have less chance of overuse injury than if you added runs.

That's true but I find the BT plan (at least the silver one) a little light on runs.  So in my case I was already planning on adding an extra run, but I have the base to handle it.  You never lose by adding an extra bike instead though.

My own approach will only change in that I will modify a few of my bricks to be run-bike-run. Like 30-min/90-min/30-min. I think my legs will appreciate it, come "race" day.

Anybody know what the run-bike-run distances will be?

Last I checked they are still trying to settle on the lead in run.  Rest is the same.  They are posting fairly regular updates on Facebook.  They are also working with DCB Aventures to get everyone an OWS if they want it.  Two races to choose from.  A little far for me but I might try and make one of them.