You can override one element - Right click Override Graphics in view > By Element
Or EOD
Or Modify>View>Override By Element
However it's not a good practice, cause you won't know which elements have been modified or not (except it will look slightly different 🙂 - But in a large project it's a needle in a haystack)
Much better way is to use filters - Some people add parameters to all elements that allow them to create rule based filters (For example a Yes/No parameter like "Heavy Line North Elevation", "Thin Line North Elevation", etc..."
This is definitely the most consistent way of doing it, but it's an extra level of management.
You can use selection filters as well, just select the elements you want to override, save the selection and use it as a filter in VG.
The main benefit of using filters rather than overriding elements one by one is that you can easily check which elements have been overridden, add or remove items and apply the same filters to multiple drawings.
Also, for finer control of lineweights in elevation, use the linework tool - Modify>View>Linework
