Customizable Phone Scripts - Sport

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.

Snowclone: A snowclone is a customizable formulaic phrase that consists of a framework that can be adapted for different situations by changing some of the words. It's typically expressed in terms of the invariable part of the phrase with blanks represented by X, Y, and Z, for example, X is the new Y. We need a term to describe an element with an customizable look (for example, if it's a text, one can customize its font and foreground color). Can we use the term "stylizable" for that?

customizable phone scripts, 6 "Colorizable" sounds awkwardly long. I would personally go for the simpler, " Colorable ", or " Ready-to-color ". Depending on the context though you might be able to stretch out and use something like "Customizable" or call the images "Templates". If your software is in insurance domain and can process a million forms under a minute then powerful makes sense but if it provides high customization options, Scalable or customizable sounds great.