How would I change the command to search for alt anywhere in the note?

Like if it's:
Herb/Alch Rusky's alt

Also can I search for multiple stings like:
alt Rusky
alt Rusky's
Rusky alt
Rusky's alt

Basically a list or tutorial on how the filters work would help me a lot.

It's hard to make a regex that detects multiple patterns. The first 2 would be caught by the following:

/alt (\w+)/i (Match 1)

The third would be caught by:

/(\w+) alt/i (Match 1)

The fourth:

/(\w+)'s alt/i (Match 1)

The last 2:

/(\w+)('s)? alt/i (Match 1)

Potentially, all 4:

/(alt (\w+)|(\w+)('s)? alt)/i (match 2, I think)

When making regexes like these you should study the matter a bit and test thoroughly. It's always better to have consistent notes and not use regexes like these.

The last one would act unpredictably in a note like:

Leatherworker alt Rusky