I would like to force Lion to show both Excel and TextEdit as applications in "Open with..." dialog. I currently have Excel set as the default for .dat files but occasionally I just need to glance at the header of the file which is much quicker with textedit. It is a Space separated text file. On that same vein, is it possible to have the finder recognize the file as text so I can preview it? Even if I set the default app to TextEdit it won't preview. I did find On OS X, how do you change a file's "Kind"? but it doesn't quite address my request. Thanks for your help.
Checked out the link from @slhck and did it slightly differently.
/System/Library/QuickLook/Text.qlgenerator (right click...Show Contents) to include
public.csi and now preview works. I did have to give myself permission to edit the file (Get Info...Sharing & Permissions...Everyone- R&W) and I have XCode installed so I used property list editor to add the additional UTIs to Text.qlgenerator.