Based on the ruling I am reading here viewtopic.php?f=59&t=68801&p=889197&hilit=unexpected+betrayal#p889197 Unexpected Betrayal modifies each army's force. Since this would add force to one and take force away from the other would it be considered a force bonus and penalty. And if so would Justly Earned Victory's ability to negate all force bonuses and penalties negate the force swap from Unexpected Betrayal?
Unexpected Betrayal and Justly Earned Victory
A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
Unexpected Betrayal modifies each army's force.
Not always but it may do so if its target remains opposed at the current battlefield until this battle's resolution begins and armies' Force totals are calculated.
Since this would add force to one and take force away from the other would it be considered a force bonus and penalty.
No per Card features, Maximum and minimum values, bonuses and penalties: "Changes in total Force of a unit or army which are not due to changes to the Force of its component cards (for example, a Follower being destroyed or bowed) do not count as Force bonuses or penalties."
And if so would Justly Earned Victory's ability to negate all force bonuses and penalties negate the force swap from Unexpected Betrayal?
No. Unexpected Betrayal's effect is neither a Force bonus nor a Force penalty to a "card at this battlefield" (Justly Earned Victory's text) therefore Justly Earned Victory's second Battle action does not negate it.