This is not user-configurable. I maintain an XML file which defines all file formats supported by IMatch, and for each file format a number of settings and options. One of them is if a file format is using WIC or not. For example, I explicitly define that IMatch does not use WIC for JPEG files, even if a WIC codec is installed. IMatch handles JPEG files with the built-in JPEG decoder much faster.
During startup, IMatch asks Windows for all installed WIC codecs and the file extensions they support. From that list, IMatch removes all file formats with an explicit "WIC disabled" flag. If IMatch now encounters, for example, a NEF file (which is marked as requiring WIC) but no WIC codec is installed that handles the .NEF extension, IMatch displays the message. But only once per session. And you can disable it as well.