`eucast_rules()`: add inverse of `overwrite`

[msberends]

Description

Hi Matthijs
 
I’ve decided to write up a custom_eucast_rules() for the AGAR surveillance program, and I’ve got it all working, but I’m wanting to only change the SIR results that are reported and not add any results where the reported is “NA”
 
I can see there is the argument “overwrite”, which changes the results, but there is no argument that excludes the addition
 

 
I’m also not sure I understand the explanation for the overwrite argument – it says “To ensure compliance with EUCAST guidelines, this should remain FALSE”, but then if we don’t make changes how do we include the changes from their expert rules?
 
Thanks

Use Case (optional)

No response

[msberends]

Also: explain the overwrite argument better

[msberends]

Added to the beta version