I am having difficulty transitioning a bond value function into a par value function. I believe it should be based around modifying the bond value function, but I am not seeing the process. Any help would be appreciated. After writing the correct par value function, I will have to verify it works with some known inputs.

A good way to start approaching this question would be to write out the equation for par_value giving bond_value and other parameters (I think that's coupon rate, ttm is time to maturity and y is yield.

It looks like you're maybe taking Ang's datacamp course? The chapter 1 slides walk through this process to create the bond_value function.