I wasn't recommending adding it to the file name. I was recommending adding a new field to the database so that in the Print tab of the printer, you can see a column of that chosen filament for that file. As for multiple extruders, I see that may make things a bit difficult. Currently I do add a prefix to the filename of PLA, ABS, etc. But as stated in a different bug report, changing the name affects the file links currently.