Was the algorithm changed or just a constant/variable. I'm not as familiar with how mining difficulty changes but the reward halvening is based on a relatively

Was the algorithm changed or just a constant/variable. I'm not as familiar with how mining difficulty changes but the reward halvening is based on a relatively simple algorithm that uses a constant of 210000 (blocks). Changing that constant doesn't change the algorithm but certainly changes the behavior of the system. In this case, the security of the system is clearly not changed when the constant is changed. My understanding of mining difficulty is that you could tune it without compromising security so long as it's hard enough to provide dampening to the system. Right now it's adjusted to produce one block every 10 minutes on average. Ultimately, if you want to keep the algorithm you need to either allow bigger blocks or allow blocks to be produced more often.