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could you make it so that default channels are stored as a separate INI section that can receive updates with new mIRC versions

We discussed a similar idea relating to the servers list some time ago and how this would not be practical. The only way this would work is if, after a new version is installed with a new favorites list, mIRC displayed a Text Merge type dialog that allowed users to compare/merge the old and new lists for all of the different parameters of added/removed/changed channels. For example, if the new list has #mIRC with a new network added, the user would need to be able to merge that into their existing #mIRC entry, preserving their current #mIRC settings, where they may have added a password, removed some networks, etc. Or if the new list includes a channel that they intentionally deleted from the old list, they would need to remember to not merge it in. And so on. The user would need to do this manually for each channel in the favorites list after each new update.