Does changing a parameter value in a stored procedure before the query affect the cardinality estimate?

I routinely “scrub” the parameters of my stored procedures at the top before I run the query like this:

-- Scrub params
SET @SearchText = NULLIF(@SearchText, '')
SET @ThreadId = NULLIF(@ThreadId, 0)
SET @Hashtag = NULLIF(@Hashtag, '')

But then from this article I read the following:

If the query predicate uses a local variable, consider rewriting the
query to use a parameter instead of a local variable. The value of a
local variable is not known when the Query Optimizer creates the query
execution plan. When a query uses a parameter, the Query Optimizer
uses the cardinality estimate for the first actual parameter value
that is passed to the stored procedure.

Does it count as using a local variable if the value originated from a parameter? I’m wondering if my parameter scrubbing could affect the creation of the query execution plan.

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Author: adam0101