Try in this format and see if it works for you. You will need to match the contents of a new decal folder. should be the same except the actual new decal your trying to replace.
Here is the new FPE format for decals:
;header
desc = Arrow
;visualinfo
textured = Arrow.dds
effect = effectbank\reloaded\decal_animate4.fx
addhandle = decalhandle.dds
castshadow = -1
transparency = 6
;orientation
model = Decal.X
defaultstatic = 0
defaultheight = 50
scale = 300
materialindex = 0
cullmode = 1
collisionmode = 11
;statistics
strength = 0
explodable = 0
;ai
aimain = decal_flat.lua
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