Apps you need : Go Weather EX and APK Editor from Play store.
First you need to collect weather icons on your folder(any) in internal storage to choose from..
I choose icons I need and placed in a folder I created as 'Images'.. name of icons won't matter..
1.Open Apk Editor app and choose 'Select Apk from App'
2.choose Go Weather EX
3. Click on Resource on bottom. it will open apk file..
4.choose drawable-hdpi folder to open(those icons for panel)
5. you have to scroll far down to find icons you need to edit..
any icons with 'notify' name you need to edit as shown below.. I only edited white icons, with matching weather..
Just click on a icon you need to change and it will direct you internal storage to find a icons you need to replace.. then find a folder you stored your weather icons...
6.another folder you need to edit for notification weather on status bar..
7.same direct as above.. again you have to scroll far down to find icons you need to edit..
once you done replacing each icons click Save on top right button and it will sign back apk..and your editted apk will be on 'apk Editor folder'
8. before you install with your apk, you need to unintall orginal Go Weather EX first.