Alternatively, you can edit the urls in the Kobo eReader.conf file. Seems more simple, permanent and safer than patching binaries:
Since I don't use the kobo store or any online service from kobo, I disabled everything on that configuration file and never had any upgrade, error popups or anything from kobo.
Don't ask me which variable preventing the upgrade, I have no idea, I just wanted to disable all online services from kobo.
Code:
[Services]
ContactUsURL=http://127.0.0.1
EulaURL=http://127.0.0.1
FirstTimeUXURL=https://127.0.0.1
ForgotPasswordURL=https://127.0.0.1
ImageHandlerURL=http://127.0.0.1
PartnerProxyHandlerURL=https://127.0.0.1
PrivacyURL=http://127.0.0.1
PurchaseURL=https://127.0.0.1
RequestURL=http://127.0.0.1
SecureURL=https://127.0.0.1
ServiceDomain=.127.0.0.1
SignInURL=
SocialAuthorizationURL=https://127.0.0.1
SocialURL=https://127.0.0.1
WebsiteURL=http://127.0.0.1
WebstoreProxyURL=https://127.0.0.1
WebstoreURL=http://127.0.0.1