Here I'll post details, guides and demonstrations on how it works and how to use it. Please note the videos and images from three weeks ago are prototype stages and may not visually match final look.
As a rule of thumb VariTech parts are always 1x1 sized parts with a white box which is visible in blueprint mode. The white box is the actual part size on the build grid. Ordinary or other mod parts may not work together with VariTech parts especially if a TechLevel locking system is involved or the need of crews.. It's not that it's impossible it's just they don't go well together.
The idea for the mod was originally envisioned more than a year ago based on animation and limited possibilities for morphing parts. As the game has improved and changed with new features so has the design to accomplished these. Also adjustments has been made to accommodate building compatibility with Kroom's Forge mod. However, both mods are not visually compatible. The reason being Kroom's mod is frankly not truly designed for auxiliary craft and fighters being tucked inside ships and not obstruct the roof. It follows vanilla's ship design layout, hence, there will be mismatches with this mod. This mod has always been designed with auxiliary craft and fighters in mind to fit visually into a ship and accommodate complex animations, hence, the use of all layers as well as different layout to vanilla's.
Due to game engine changes in 0.14.0 it's no longer possible to overlap graphics in one layer according to order. Therefore, graphics have to use more layers to avoid visual clipping glitches The complexity has increased and also requiring more layers to accommodate additional functions. This can be resolved with custom layers. But due to repercussions on memory and increased lag adding additional layers it is currently not an option. This option may become viable in a few years when better computers are available to most players. So the current compromise it to use all layers and with some tolerated contested glitches. Although, this expansion has reduced the distance to vanilla layout, hence, Kroom's Forge mod it's still a difference of two layers for the important "roof" view.
The original fixed size and building lore has changed to accommodate and use parts from Kroom's Forge mod and is now open. The original idea was to prevent misuse and abuse, keeping to a small size building lore and accommodate the nature of morphing parts. With this open design the morphing aspect is no longer viable without the player's building cooperation. This means the player still has to follow building conventions and lore to accommodate morphing parts visually. This is still designed around a core section and should still limit misuse and abuse if used accordingly. This also may still support the original intention of allowing the mod to easily transition toward being a fighter mod when Cosmoteer introduces and supports fighters within the game.
As this mod is not a single part mod and is tailored toward mechas, variable fighters and similar systems building has to follow certain placement to complete properly. The placement is very important as they require a lot of special interaction between parts. Their interaction and functionality is range restricted to avoid interference from one end to the other.
The building placement may change slightly between mechas and variable fighters in general, but part size will play a minor role for non-form related parts (visually non-mecha, non-fighter parts).
As all actual parts forming the mecha or fighter will be a fixed size of 1x1 the core section will remain the same. Arms and wings may have to be moved to fit depending on visual appearance.
FAST pack, and similar backpacks have to be placed below the legs and fuselage / back parts. Some of these packs can have optional parts that are placed on a certain side. A disconnect sign will appear if these are placed wrong.
Some packs will disable transformation like the fold booster packs. These have to be ejected (eject/jettison button) before transformation can be used again. A fold booster pack is required to FTL. After ejection a fold booster can be recovered by repairing it (at low cost).
The variable fighters can have weapons under the wings which have to be placed beside the wings. Wings have a certain load which will restrict the number of weapons based on their weight. This feature does not apply to parts from Kroom's Forge mod.
Also the number of weapons will restrict the wing's sweeping angle. They may not fold when in boosted flight or sweep out when overloaded (for increased lift within an atmosphere). Some weapons may be placed over the shoulder by placing them below the legs. These are marked in the tool tip as "over shoulder wing" or "top". If such an ordnance it mounted FAST packs may not be mounted.