Does Divine Sanction overwrite your own Divine Challenge?

Question

So a Paladin technically has two different special marks, Divine Challenge and Divine Sanction. Some effects only work on your Divine Challenge target, and Hybrid paladins deal less damage with their Challenge than their Sanction. If a paladin puts his Challenge on something and then uses a power that inflicts Sanction, does it overwrite the effects of the Divine Challenge? Which duration and set of associated effects do you use?

Can you choose to not apply your divine sanction from a power? covers overwriting another person's mark, but I'm not sure if it's relevant towards overwriting your own mark. Also only worried about powers that don't give you the option to simply not apply the Sanction, since you could obviously just not apply it to avoid overwriting.

Answer 1

Yes. Your Divine Sanction will override your Divine Challenge.

From the Divine Challenge entry in the PHB, on pg. 91:

A creature can be subject to only one mark at a time. A new mark supersedes a mark that was already in place.

On pg. 82 of Divine Power, the Divine Sanction section reads:

Unless otherwise noted, the mark ends before the specified duration if someone else marks the target.

[...]

Divine Sanction is meant to complement divine challenge. You can use divine challenge to mark one creature and use divine sanction to mark others. Divine sanction has fewer restrictions than divine challenge so that you can easily use the two in concert.

This tells us that Divine Sanction is a mark that behaves like any other and cannot co-exist with another mark on a given target (unless the particular effect explicitly states that it can).

It does not explicitly state that you can apply both the Challenge and the Sanction marks to a single target, thus the general rule of "one mark per target" applies.

Regarding the second part of your question, unless the particular power allows you to forgo applying the mark, then it will be applied and will override any existing mark that you or someone else has in place on that target (unless the effect explicitly states otherwise).