If you look in the pkg file there is also a 3.55 EBOOT.BIN, so just use multiman or FTP to change the EBOOTs over once the pkg is installed.
That said not a lot of point installing it on 3.55 as 3.55 can not decrypt V4 SDATs. We can already decrypt V3 SDATs on the PC. The decrypting is not the issue, we have been able to decrypt V4 SDATs since we got 4.XXCFW. The re-encryption to a V3 SDAT that 3.55 can use, that was the part that we were missing. Now using my SDAT Creator you can now do this.