In this case, 変法 is translated as procedure or method.

There are many references on the net to the "modified Lowry procedure" or the "modified Lowry method" (as opposed to the standard Lowry procedure).

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Note added at 3 hrs (2009-10-04 13:00:23 GMT)
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Examples:
- Recording of absorbances need only be done within 10 min. of each other for this modified procedure, whereas the original Lowry required precise timing of readings due to color instability.
- A modification of the Lowry method for detecting protein in media containing lignocellulosic substrates


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Note added at 3 hrs (2009-10-04 13:13:26 GMT)
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Excuse me for missing one word "modified" in my above explanation.
I meant 変法 is translated as "modified procedure" or "modified method."