At its core Liliths Throne is really just TiTS. The most major additions to the formula are the ability to create your own potions, persistent generic encounters that you can bring home and one giant generic sex scene instead of a lot of custom written ones. Innoxia has stated that the game is deeply inspired by TiTS's predecessor, so its not really a secret.
Its not really looked down upon to take core systems from other games and apply them to your own, even if you copy almost all of it. What matters to not being a copycat is to give a new spin on these systems, maybe create some systems of your own, and wrap them in a different story.
The transformation system in these games are really not that big of a deal, its mostly just making a model of each possible transformation position, then writing text for when the character transforms into that, text for describing the transformation, and some tags like "furred" and "scaled" so you can check for certain types of transformations.
The difficult part of this system is that each possible transformation is a promise that you will consider them when writing scenes, so you'll always have to ask yourself what possible transformations the player currently has. This is why writing for these kind of games takes significantly longer then a game where the player cannot transform.