This question keeps coming, for example people on vita OFW 1.69 are asking us how they can update to 1.81 without running the risk of installing the latest firmware 2.01 instead.
The Z made a tutorial on how to do this exactly. Keep in mind that this does not allow you to downgrade, only to upgrade to any version you want. You can reinstall your existing firmware, or go up to any version, but not go down. This is nevertheless useful for people who were on a fairly old firmware and want, for example, to try and install total_Noob’s CEF on 1.81 with the latest technique that we describe here.
The Z’s video is fairly old, but I never blogged about it, and now feels like exactly the right time for that In addition to this, The Z posted a fairly details Tutorial on /talk. The tutorial is fairly long, so I will simply link to it:
You will need OpenCMA, and a working http link for the update file you want to install (for example, the 1.81 OFW Firmware). The Z provides some links in the tutorial above with everything you need.
Note that if you don’t have a working http link for the file, you can still run a local server on your computer and use a proxy to trick the vita in downloading the file directly from your computer (well, that solves the issue of the direct link, but not the issue of finding the firmware file in the first place… again, google is your friend), but that is out of the scope of The Z’s tutorial.
The basic idea is to install OpenCMA, and trick its firmware file into believing that a firmware update is available. That update will actually point to your own version of the firmware.
The explanation is fairly technical, so don’t expect a “push a button and be done” type of system here.
For those of you who don’t want only the text version at the link above, enjoy the video: