Dop-ios-mod should default to ios36, and provide a means of installing ios36 with fakesign patch. Since you are already softmodded, you can use ios249. Just change ios36 to ios249. Then it gives you the option to install ios, system menus, channels, check boot2 version, scan system.
First install ios70 with patches. The app will display what version ios is installed, and the version it would install if you wished it to. So if you wanted to update your ios files, you could start at the lowest number and compare the versions, if a newer version is available you have the option to install it. When you install your ios, it will ask if you want to patch them. Typically only the system ios and ios36 should be patched, so don't apply patches on the rest. If the ios is not on your wii, you probably don't need it, but installing all of them wont hurt, but will waste blocks. Most ios only take 1 block, some of the small # one take around 13, so not much space. You'll probably want ios33, 53, 55, 61 to be updated, and don't forget to install ios70, with patches, and ios36 with patches.
Once you've install your ios, goto system menu's and install 4.2 in your region. If you where to brick your wii, this is where it would happen. So cross your fingers and hope to god your power does not go out, bad news if it does.
Channels- you can update any channels you wish to use, like the mii channel and shop channel, what ever you like.
Remove stubbed ios- this option removes stubbed (useless) ios files. This frees up space, and allows the re-installation of the useful versions from official disk updates, if you ever wanted to do that. It is optional.
You should not experience any comparability issues with your softmod. HBC and others will still function as they should. The only exception is system menu hacks, and methods to apply them. There are various options depending on your system menu version.
If you wii supports boot2 bootmii, it would not be a bad idea to have that installed first. When you done you probably would benefit from installing priiloader.