Firstly let me thank you for your contribution, your question has indeed shown an area of the rules that hadn’t specifically been defined and rest assured that we will ensure gets a rules amendment that will help the game run smoother.
Let us start with answering your specific card questions
Martyrs Cry. You are correct this is for only this round of the shootout.
No Turning Back.Again you are correct, this is until the end of the shootout.
Turtle’s Guard.You are once again correct the token remains in play until the condition on the token has been met.
Follow up to Turtle’s Guard. The token gains harrowed until the end of the shootout.
Hand rank modifiers in lowball. These apply until the hand has been resolved, just as in a shootout with a cheating hand with Barton that gets bottom dealt still retains the +1 hand rank.
We will be issuing errata at the point we get the proper rulebook definition to ensure the cards act as the rulebook want’s them to.