Hi, started to play with OpenWRT on a raspberry pi 4 but can not install the 2nd nic (usb). I have both a rtl1850 chipset and a rtl1853 but when i go to install the appropiate opkg package i find I have a later kernal version than supported 
now I have read this is a feature of the type of image im installing which is a snapshot of the latest software precompiled by robots. Now I am to much of a noob to roll back my kernal version, so Im am left wondering the best way forward ? Do I keep trying new snaps each day (seems like a lot of work) or is there an archive of previous snaps so I can pick one with the appropiate kernal version ? Or perhaps the alternative to the snap is around the corner? I am keen to continue and just hoping for a possible roadmap. Any assistence is appreciated.
Flash a new image and grab the packages that come with it at the same time. Those are the only kernel modules that will be 'in sync'.
I believe images are built almost daily; already one day later you might be unable to install modules. The package manager checks the hash the kernel and module package use, they need to be the same.
Very sorry Borromini, your answer exposes my ignorance. "Flash a new Image" ? do you mean download a new snapshot ? As that seems to be the only option available for a raspberry pi 4
or are you saying that i should be downloading the packages at the same time as I download the snap image ? I hadn't thought of that.
see item 3
snapshot overview
Yes. See also Wulfy's link for how snapshot builds work.
I wonder why they keep all kmods in https://downloads.openwrt.org/snapshots/targets/bcm27xx/bcm2711/kmods/
for those who know how to deal with mismatched and broken dependencies... and are prepared to brick a system and own it.
Thanks guys, for leading me to the answer, which is of course in the documentation once I understood what the question was.
So to paraphase in language that may assist someone in the future.
Once you flash with a snap image, try and install any kernal type packages within the same 24hour period before the next build.
Due to the small size and ease of installation this is not as onerous as it first seems.
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I think there is a better way to be time independed: just download everything for your target from the snapshot repository to your local disk (wget --recursive is your friend).
This was about 1.8 GiB for the rpi4b January-2020 snapshot. You'll get a consistent set of packages and (most import) it stays consistent all over the time.
That does work indeed, but that will strain the resources OpenWrt has. Snapshots are by their very nature volatile. If you would like to stick longer with a single snapshot, it's actually better either to use the image builder to include the packages you need (which still leaves you out in the cold for the odd kernel module if you'd need it down the line), or just run your own builds.