I will try to break up your string-questions into bite-size pieces.
Question here is there any possibilities to get rejection in Personal Appearance.
FC: Yes, there is always that possibility. With a good lawyer helping you the chances are reduced.
Will US Consulate treat this extended petition same like fresh petition and may reject?.
FC: Yes, although they will be aware of the prior approval, they are not bound by it.
Please advise what would be advantage of having visa extension done in USA and will give some hope to get the stamping without any issues in India.
FC: This question makes no sense. You can not get a visa stamp in the US and, according to your facts, you have already extended the I-94.
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The consulate will make its own determination on the L-1B. Having had USCIS approval should be helpful but It all depends on the consular official.