Do you leave your BOM in solidworks or do you export it afterwards? If you make a macro to export it in excel it should be possible to add the desired rows to the excel table you will have generated.
If it's only for it to appear on solidworks I have no idea.
To be honest, I don't feel like you can do all of this with a bill of materials.
In addition, from a visual point of view, I'm afraid that your nomenclature will quickly become illegible (well, that's a very personal vision)
On the other hand, I'm afraid that if you enter a VBA program to do it, your computation time will be prodigiously longer each time you open a drawing with a large assembly.
On the other hand, as @Martvy proposed, why not export your nomenclature in excel (right click => save as). You can then rework it as you see fit without weighing down your drawing.
And in these cases, it is easy to make a macro to sum the weights of each material, to put in red above a certain value etc etc
It's dangerous to have nomenclatures outside of SW. Even more so if the values are filled in "manually". The risk of error and the obsolescence of the data will make them unreliable over time.
Especially without any link between them.
To simplify, it's exactly as if your subjects were filled in by hand in the workshop. Well, I'm caricaturing a bit here.
Fully agree with @coin37coin, we work in this way: the project managers record their bills of materials in excel and a macro sums the identical parts, distributes them between different tabs (machined parts / trade), adjusts the layout, ...
The advantage is that buyers also have macros that allow them to sort the parts according to other criteria that are useful to them
Indeed, you don't want someone to modify the files, but between conscientious people it goes well. I don't remember any problems at this level for ±10 years.
So it's prog on excel, a little simpler than under SW and the possibilities are more extensive.
I don't want to say it's the best solution but for us it works...
If I understood the question correctly, at the level of the BE there is generally no information that does not come from SW. Sometimes we add in the nomenclature if a discussion on the feasibility has been carried out with a subcontractor so that it can be assigned, rarely more. (except for "messed up" files but here in general Murphy keeps them....)
Ah, yes: the coefficient. If several identical tools, the macro multiplies the quantity.
The big interest is the transmission of data with the possibility of work by several departments. We avoid that buyers copy component refs from printed names or pdfs because the errors are there (there on the other hand there is experience in 3 years with a partner ;-) )