Isn't there also a way to directly add one tissue onto another? Something to do with [TISSUE_LAYER:BY_CATEGORY:ALL:FLUFF] (taken from my fluffball mod), perhaps?
See that adds the tissue over "ALL" BP's which means (Brain, Heart, Lungs, Spine, Guts, Skull, Etc..)
you have to think of [TISSUE_LAYER:...] as painting a wall. if you want a tissue under everything, Paint it first. Because every other tissue added after will cover it.
because the tag works like this
[TISSUE_LAYER:type:parameter1:parameter2]
type := BY_CATEGORY or BY_TOKEN
parameter1 (category) := selects a bodypart(s) by the category it is defined in like "ARM_UPPER" which is both RUA and LUA (right upper arm and left upper arm)
parameter1 (token) := selects a bodypart based on it's token like RH "Right Hand"
parameter2 := this is the tissue to add to the selected bodypart in "parameter1"
my notes that I copied from the wiki long ago say there is a location parameter "parameter3" which to me is only for really attention to detail things like eyelashes being on the front of an eyelid (cause having an eyelash in the eye hurts "in DF don't matter" this is a more of a extra thing that is unneeded)
Location Non-Arg are: FRONT, RIGHT, LEFT, TOP, BOTTOM.
Argument locations are AROUND and CLEANS
Also note this: the AROUND seems not to work on a BP defined as a UPPERBODY but the desired effect of having something around something is the same as just making it a LAYER (aka leave out "parameter3" as it's basically not important)
There is a TISSUE_LAYER_OVER and TISSUE_LAYER_UNDER (is helpful in the cases you want to just add something under the topmost layer "skin" from a body_detail_plan) the _OVER to me seems redunant (unless next version you can target a tissue layer)