If or when you tackle this, you should probably keep some things in mind:
While you say you want it to be a small project, I think it may be best to try to be as in-depth as possible when writing the item (this goes for any transformation item in the game). Sure, there is a place for simple transformation items that do specific things, but for something like a bimbo-centric transformation, you should probably think about putting a lot more into it.
For example, making a scene that simply reads as "Your hair tingles. Your hair is now blonde!" is a bit too much on the basic side. That text should probably have descriptions of the mental and/or arousal state of the character undergoing the transformation. An example of the difference would probably be Lip Tease (where the changes are only cosmetic), as compared to Horse Pill, The Treatment or Laquine Ears (where the changes are internal and functional, and have a stronger connection to the mental/arousal state). Essentially, you want to have a descriptive lead-up and tie potential (sexy) consequences to the changes that happen. Of course, you don't have to choose to have a change-over-time aspect like the examples I've mentioned, but that style of transformation does help illustrate the progression instead of an automatic instant-change.
I think an easy mistake to make for writing for big transformation items is having simplistic A to B transformations--which again, have a place in the game--instead of actually painting out a scene to show the effects of going from A to B to make it a worth-while read as well as a satisfying result of the transform. From what I can gather, you have a higher chance of catching Fenoxo's attention with sexy TFs more than simple ones.
For a bimbo-transform item in particular, you should ask yourself: What makes a bimbo sexy? How will these changes affect the character? Why do the changes happen and at what cost, if any? Is it purely just a cosmetic transformation or is there more involved? When writing, answering these questions along the way may help with illustrating the scenes a lot better. Most importantly, make it as sexy as you can--this is a smut game after all.
In my opinion, an item that does incremental changes may be best for a player wanting to tailor their character to their liking. However, if you want an all-in-one go on use, there isn't anything wrong with that either. Or you can have both as alternate variants (similar to the Pandaneen and Panda Pro items, or the Amazona items).
I hope this helps and best of luck to you if you decide to write for this project.