Yes, you can if you want to.
WARNING: Do it at your own risk, do not blame me, or anyone else if you screw up iGuidance.
What you need? iGuidance software, ofcourse. HexEditor (I use XVI23)

- Copy iG V2.x map folder to iG V3 installation folder (C:\Program Files\iNav\iGuidance\Maps). Make sure you make a backup copy of the maps folder for both version.
- Run iGuidance.exe or iGuidanceUMPC.exe and it will throw an error on you. Notice of an error. Wrong File Version Data file: linkinfo.bin: LI0X!=LI07. Basically it said that you can use previous map version in iG V3.
- Write down LI0X where 0X is the linkinfo file of your iG 2.X. iG V3 linkinfo is 07. Click okay to close the error (iGuidance exit).
- Open linkinfo.bin file in your Hex Editor and search (Text) for LI0X. It's the first 4 characters of the file. On the TEXT side not HEX.
- Change LI0X to LI07.
- Save linkinfo.bin and close the file.

- Run iGuidance.exe or iGuidanceUMPC.exe and it will throw another error on you. Notice of an error. Wrong File Version Data file: name.bin: NM0X!=NM02.
- Write down NM0X. Click okay to close the error (iGuidance will run BTW).
- Open name.bin file in your Hex Editor and search (Text) for NM0X. It's the first 4 characters of the file. On the TEXT side not HEX.
- Change NM0X to NM02.
- Save name.bin and close the file and close your hex editor.