[Android Q&A, Help & Troubleshooting] JonW434:
Yes, it's sort of amazing. I've had this phone since around 2015, can't remember exactly.. but to think that it's now 2020, and it's still has people using it, or talking about it, or providing any information or updates at all, I'm new to the world of tinkering with smartphones, but it's very surprising to me.

In the last week, I've now tried two different roms, and outside of some minor niggles (that most likely will be resolved without too much trouble), in both cases, it's the best the phone has ever been. The new battery finally went in today (I wanted to get a baseline with the old one to see the difference it makes) and that helps, but the OS itself.. and all of the work that has gone into the evolution of these things.. thanks to all involved, for all those who have posted in this thread over the years. And for those who continue to keep the phone alive. It's especially amazing to think that in 2020, it's still getting proper security updates for the OS. In the same way that a Microsoft or Samsung gives official updates. It's great, so thanks to fwiep for that.

In terms of adb sideload, if anyone is curious.. I tried initially and didn't think it'd work. It would say things like "zip is corrupt", or not even find the device at all. The adb driver (or my usb hub) was acting a bit silly, and making lots of noises (disconnect, connect, disconnect). So I decided to go find the CWM universal adb driver. I think I was using the one that came with HiSuite beforehand. That seemed to help, and then when trying to load the zips (can't do img files apparently) it said something like "you need a later version, adb must be at least 1.0.32". So I searched around and found this here..

https://androidfilehost.com/?fid=95784891001607611

And then it worked. The main reason I am mentioning this is because of the sticky on the first post, the AndroidSDKSlim contains the earlier version of adb.exe that won't work with the sideloading (with twrp 3.0.1-0_unofficial). But this version will..

The only downside I had, was that it can't change twrp versions from within recovery. It needs a zip, and for y550, they all seem to be .img files. I had no luck with that, and if I needed to change twrp version.. I would have needed to install the correct OS rom (any that will work) in order to get back into USB debugging in the system itself.. and then do the fastboot boot twrp.img etc. Thanks to Saint_13 for the partitioning info, that might in handy in the future, will save it to a text file for future reference. My disk has the same name btw. I expect the walls of text to start shrinking a bit now, as I need to get some intensive testing done on a few seperate things, but if I have any big breakthroughs or positive things, I will report them here incase anyone wants to try a similar thing. In terms of temperatures, I've figured out that the super intensive sites that hit the CPU hard.. it's best to use them in short bursts when the phone's been idling with the screen off (35-40C). They can handle them fine. But if it's already hot after a lot of restarts, or installations or whatever else.. avoid them until the phone cools down.