Win 98 file type

I have a text file that I need to rename and change the file type. Right now the file is test.txt I would like to rename the file and also change the file extension so that the file will be test1.1007 The 1007 is today’s date. I can successfully rename the file in Winexplorer, but no matter what I do it remains a txt file. I have opened the file in wordpad and done a save as, then changed the name to test1.1007 and changed the file type to all files, but it still results in a text file. This is going to be a daily process, so tomorrow the file will be test.1008 then test.1009, test.1010 etc. How do Iget this to be a .### file vs a .txt file every time?