You Cannot Downgrade To iOS 10.2 If You Have Already Updated
Users should be warned that if you update to iOS 10.2.1 and find that there is some issue with it then you cannot switch back to iOS 10.2. That is why we advise people to wait a while before making such updates. But if you are someone like me who cannot wait then you will be pretty much stuck with iOS 10.2.1. Why is this important? It is important because iOS 10.2 can be jailbroken while the newer version cannot.
If you are still on iOS 10.2 and have managed to not update to the latest version then I would recommend you to save your SHSH2 blobs. By doing so you will be able to switch to the firmware that Apple is not signing currently.
You can use Yalu jailbreak to jailbreak iOS 10.2. If you are reading this article then chances are that you already know what you have to do. Yalu jailbreak is semi-untethered which means that if you restart you will need to jailbreak again. This can be a pain but given the benefits of jailbreaking your device, it should not matter much.
It should be noted that this jailbreak is still in beta so there might be some hiccups here and there. It is unstable but should last you a day at least. The point to be noted here is that if you are going to be jailbreaking your iPhone then you should avoid iOS 10.2.1 at all costs. Once you upgrade there is no turning back and there is no jailbreak for 10.2.1 as of right now and you will have to wait.
iOS 10.3 is in beta as of right now and word has it that it should be out in a few weeks, we do not know what it will hold for the jailbreaking community but we will find out in time.