Note: I am not a lawyer.
You are misinterpreting the "as-is" clause. "As is" does not mean you cannot modify the code (such a clause would, in fact, go against both the spirit and the letter of the Apache License). "As is" is a clause that states that the code you're using is what it is, and you need to execute your own due diligence when you use it. E.g., you cannot sue the Apache Foundation if a bug in Commons Lang crashes your application. Wikipedia's article, while not a legal source, explains this concept quite nicely:
As is is a legal term used to disclaim some implied warranties for an item being sold. Certain types of implied warranties must be specifically disclaimed, such as the implied warranty of title. "As is" denotes that the seller is selling, and the buyer is buying an item in whatever condition it presently exists, and that the buyer is accepting the item "with all faults", whether or not immediately apparent. This is the classic "buyer beware" situation, where the careful buyer should take the time to examine the item before accepting it, or obtain expert advice.
By renaming the package, you are creating a "Derivative Work" of Apache Commons Lang. Section 4, Redistribution of the APL-2 clearly states what you need to do in such a case:
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B. You must cause any modified files to carry prominent notices stating that You changed the files; and
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