While we do not yet have an adjustment scheme for spells in place on the Play tab yet you can use the "Armor Statistics Adjustment" in the Adjustment Table to modify your existing Armor in the manner described in the Spell itself, This Adjustment should enable you to tweak the EAC, KAC, Speed Adjustment, Max Dex, and Armor Check Penalty as appropriate.
Could you please submit this feature request to
support@wolflair.com so we can put it before the devs? Thank you much!