Yes and Yes but I want to qualify and expand on my answer to the first question.

Why do we have WPS's ? - to assist the welders and also to control the welders.
If you give a welder a WPS for 2.5 mm electrodes but tell him he can use 4 mm electrodes what is he going to do ?
Weld with any amps he feels like.
You can weld with 4 mm electrodes without having to requalify the procedure but you must revise the WPS (refer QG-101, QG-105.4, QW-101)

And every now and then you will see a WPS with something marked essential that isn't in the Sec 9 list.

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P.E. Metallurgy, consulting work welcomed

The welder is bound by what is permitted by the WPS. Whether the WPS is correct or whether it is wrong, it is the document that tells the welder what can be done in production.

If the WPS only lists one electrode diameter, that is what the welder must use. If a range of electrode diameters are listed on the WPS, the welder can use any diameter permitted by the WPS.

The WPS must address all the essential and nonessential variables, and if applicable, (when CVN is required) the supplemental variables.

If production requirements necessitate the use of a larger electrode diameter, the WPS listing a single electrode diameter must be revised to include the larger electrode diameter before the welder can use the large electrode in production.

If the revision of the WPS involves an essential variable beyond the range that is permitted by Section IX, the WPS must be requalified to include the change that involves the essential variable. The same is true with a supplemental variable, but remember, the supplement variable only has to be considered if CVN is required by the construction code.

Sometimes people confuse the WPS with the PQR. The PQR is a record of what was done to qualify the WPS and it also lists the test results. The PQR must record all the essential variable and where CVN is required by the construction code, the PQR must also record all the supplementary essential variable. With regards to the nonessential variable, while the Section IX does not state they must be recorded by the PQR, there are many times that information is useful.

"What was the groove angle used when you qualified the WPS for GMAW?"
"I don't remember, it is a nonessential variable, so it wasn't recorded."

"What amperage did the welder use? I need to list the amperage range on the WPS."
"I don't know, it is a nonessential variable, so I didn't record it."

"What voltage range did the welder use when he welded the test assembly for GMAW?"
"I don't know, it is a nonessential variable"

I think you can see that some actual data considered to be a nonessential variable might be useful when writing the WPS or if there was an unacceptable test result. Was the root cause of the failure due to the groove angle being too small? Was the failure due to excessive root opening, insufficient voltage or amperage?
"What needs to be changed to pass the mechanical tests? I don't know. I didn't record it because it was a nonessential variable."

Best regards - Al

WPQR's are more often than not only as much worth as their pWPS'ses.
A well-documented pWPS helps a lot later in life, as clearly stated by gtaw.

Also, be aware that 90 amps with a 2.5 mm elektrode will give a very different cross section (penetration) as 90 amps with a 4 mm electrode.