Yes, you can convert, but you will have to do some manual manipulation. Have you read the Pioneer protocol help in KM? It says:
Pioneer 2CMD:
If some of the functions for your device send a two-part signal
where the device code is the same but the command code varies, you
need to use the Pioneer 2CMD protocol.
For the functions that only use one command code, enter the same
command in both the regular OBC/EFC column and the byte2 column of
the Functions sheet.
For the functions that use two codes, enter the first one in the
OBC/EFC column and the second in the byte2 column.
Pioneer 3DEV:
If the functions for your device use one of up to three different
device codes, and some of the functions even send a two-part
signal as described above, then you need to use the "Pioneer 3DEV"
protocol.
Enter the three device codes, and then, on the Functions sheet,
enter the command codes in the regular OBC/EFC column.
In the byte2 column enter a "1", "2", or "3" to indicate which
device code to use. If this particular function uses a two-part
signal, put a space after the device code number and then enter
the EFC or OBC.
For example, if device code 1 is 130, and the ENTER button sends a
two-part signal where the first part is device 130, command 123,
and the second part is device 130, command 133, you would enter
123 in the OBC/EFC column, and then "1 133" in the byte2 column.
NOTE: While this protocol supports both OBC's and EFC's, this
version is LSB, where most of the other Pioneer protocols are LSB-
COMP, so the EFC's will be different. Therefore, it is STONGLY
recommended that you use OBC's when setting up the Pioneer 3DEV
protocol.
So if your current upgrade is properly built using the Pioneer 2CMD protocol, you are apparently using a single device number (the default is 165 - but it doesn't really matter).
First ensure that you are using OBCs rather than EFCs (on the functions worksheet, if necessary, click on swap EFC/OBC),
Then simply change the protocol to Pioneer 3DEV.
Now comes the manual manipulation.
Ensure your device number from your 2CMD upgrade is listed as one of the three devices available on the Setup sheet (for the default, 165 is device 2).
On the functions worksheet, in column C, where previously you had only the OBC for the second command (or repeated the first command), you will have to add a 2(space)in front of each second command. (Again, this presumes the default of 165 assigned to device 2. If your device number is device 1 or device 3, then replace the "2" with a "1" or "3" as appropriate.
Then you can continue to manually add the functions for the other devices from scratch.