You can rotate any entity with pev_angles. However non-bsp models can be only a box (bsp model is when model string starts with "*"). But it still can rotate non the less.
In case of bsp model, you can set entity to SOLID_BSP, then check if aiming hits it, and then restore the pev_solid (however it will not work for all entities, for example with water it doesn't work, as far as I tested).
For entities what have models set from models/ folder, there was and probably still is a guide on how to detect is player aiming on it. Or was/is that some kind of plugin what explodes grenades when they are hit by the bullet, and you can check that code.
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Skill and no annoying bugs with fixed balance issues is my goal!