If you want to go back to using the old addon, you can download the last version of Shadow4-Widgets.r2skin-addon that used MSN Weather, like from
First, rename Shadow4-Widgets.r2skin-addon to Shadow4-Widgets.r2skin-addon.zip (add .zip), and unzip it.
It's for Shadow4 1.9, but the lastest Rainlendar is Shadow4 1.10, so need modify it into for Shadow4 1.10.
=> Find the "skin" file (no extension), use text editor which support UTF-8 to open it, you will see
Change "1.9" to "1.10", then save it.
And its lua scripts is base on lua51.dll, but the lastest Rainlendar is use lua52.dll, so need modify weather.lua & rss.lua into match lua52.dll.
=> Find "scripts/weather.lua" & "scripts/rss.lua", use text editor to open them. Replace strings "gfind" to "gmatch" ("weather.lua" have two place, and "rss.lua" only has one place),
then save them.
Finally, re-zip all files and rename back.
Ooh, it seem a bit difficult if you are not familiar with Rainlendar.
If you have installed the latest Shadow4-Widgets.r2skin-addon that using Google Weather, and cannot modify it by yourself, you can download and install the following patch file, it will replace Google Weather to MSN Weather.