if you are creating a mod, chances are you will find yourself in a situation where you need to assign your custom script to an archetype. this can be done by simply adding the prop to the target archetype;
DML1

+ObjProp "TargetArchetype" "Scripts"
{
"Script 0" MyCustomScript
}and this will work just fine.. until someone makes another mod that will overwrite the same script slot on the same archetype. to avoid this situation (especially if you just need to assign an additional custom script to an archetype and nothing else, like change or remove already existing scripts), create a custom metaproperty, assign your script to it instead, and add that metaprop to the target archetype.
DML1

CreateArch "Misc Metaprops" "MyCustomMeta"
{
}
+ObjProp "MyCustomMeta" "Scripts"
{
"Script 0" MyCustomScript
}
+MetaProp "TargetArchetype" "MyCustomMeta"this will decrease the chances of your mod having compatibility issues with other mods significantly, so unless there are metaprop limitations that are preventing you from being able to do this (need to apply the "don't inherit" flag, for example), it is highly recommended to assign custom scripts in this manner.

Adding scripts dynamically at runtime does unspeakable things to the game

I'm not sure why you would think that. Several of my mods dynamically create objects at runtime and assign scripts to them. Works perfectly fine, no issues.