Definition: Given the Question and Answer pair, detect whether the answer is acceptable or not. Denote acceptable answer as "yes", otherwise denote as "no". An acceptable answer is consistent with the context in question, detailed, long, and uses general knowledge of English. Answers that are not definite and suggest a variety of options are not acceptable answers.
Input: Question: Is the word "Customizable" a valid English word? Every time I write that word, the spell checker underlines it, and it suggests using "Customization" or "Customize". I'm not a native English speaker, but that word exists in online dictionaries so I wonder why the spell checker underlines it. 
Answer: The Oxford English Dictionary in its revision of March 2012 defines it as: That may be customized; able to be changed to suit the requirements of the user. Frequently with reference to computer software and hardware. The earliest citation is from 1960. If that definition of customizable suits your purpose, then there's no reason why you shouldn't use it.

yes