Generate a model into Ltspice where we can adjust a parameter
Try this (it works in microcap): -

I didn't use the &quot;=&quot; (equate) to make these statements work but, they still work when you do use the equate (optional I guess). LTSpice might need the equate.
I think your main problem was expecting the raw &quot;10n&quot; to be recognized in the .param Rfiltre statement. Having said that, microcap will allow it. I can also keep the curly braces around Rfiltre in microcap too.