On RTM, what happens is that the original APN is overwritten.
So starting with:
[Settings] Powered=true RoamingAllowed=false
[context1] Name=Internet AccessPointName= Username= Password= Type=internet Protocol=ip
...and adding an APN with access point name of "foo" results in:
[context1] Name=___ubuntu_custom_apn_internet AccessPointName=foo Username= Password= Type=internet Protocol=ip
On RTM, what happens is that the original APN is overwritten.
So starting with:
[Settings] false
Powered=true
RoamingAllowed=
[context1]
Name=Internet
AccessPointName=
Username=
Password=
Type=internet
Protocol=ip
...and adding an APN with access point name of "foo" results in:
[Settings] false
Powered=true
RoamingAllowed=
[context1] _ubuntu_ custom_ apn_internet
Name=__
AccessPointName=foo
Username=
Password=
Type=internet
Protocol=ip