INSTRUCTIONS
In a few words, you follow this steps:
0) Keep a backup of your old PES2010_EDIT.bin (and unnamed_11.bin in case you need it)
1) Open Teams Manager and select "Open Files...". Select your unnamed_11.bin and your PES2010_EDIT.bin.
2) On the list Add/Remove/Change the teams you want. In case you add a team, i suggest you pick an ID 4000+.
3) Select "Update files..." to save changes to unnamed_11 and the OF.
4) Use League Editor to assign the new teams to the leagues you want. ALLWAYS add the team on League_8 (for national teams) or League_22 (for clubs) and on Leagues: 31, 39, 40, 41, 42, 43 (this will solve the formation issue, thanks to Tottimas for the information).
5) In-game you will see the team with Austria's emblem. Please use the in-game emblem editor to import a new one