Is Mint's Package Management Method Stable?

[Husse]

With the latest mintInstall repos are no longer changed
You don't say which Mint you use and I have not checked but there should be a version for Daryna
Open mintUpdate and refresh and you should get a new mintInstall in Daryna - it's the default in Elyssa

[Husse]

Default vs. Local

This is causing misunderstandings - but mintInstall no longer changes your sources.list.
If my memory serves me right default is the applications default and local is your sources.list - which of course is your default
The wording is to be changed later on no later than with Felicia

Also, am I correct in assuming it is potentially dangerous to update the system using methods like 'apt-get dist-upgrade' or Synaptic?

You are very correct - as we use the Ubuntu repos this may cause problems
Note - as long as you only use the Ubuntu repos of the same generation Mint and Ubuntu it's OK (like Elyssa and Hardy)
But if you add Hardy repos to Daryna and dist-upgrade you get a mix of Mint and Ubuntu with somewhat uncertain outcome....

[Husse]

In this case I think you are "overly paranoid"
As long as you have the correct Ubuntu repositories the danger is minimal (but not totally absent)
And we can't get rid of Synaptic and apt - these are basic in Linux
What we can do, and will happen if Mint develops well is to maintain our own repositories for "everything"