identify FPGA reference on board

Hi,

We use a FPGA Cyclone 4 EP4CE15F17C8N on our boards and we want to switch to EP4CE10F17C8N (pin to pin compatible) for cost and availability issues.

The FPGA is programmed at each power up by a microcontroler via passive serial configuration.
Our problem is how to identify which reference of FPGA is mounted on the board to load the corresponding bitstream.
Usually, we use a simple hardware configuration with pull-up or pull-down to identify the board revision but there is no more free combination.

So I search a way to know from the microcontroler which FPGA is mounted.

I want to test the following method :
- Try to program the FPGA (10 kLE or 15kLE) with the 10kLE bitstream
- At the end of the programmation:
○ If conf_done is OK, the FPGA is a 10kLE and is well configured
○ Else conf_done is KO, the FPGA shall be en 15kLE, the microcontroler starts a new programmation cycle with the 15 kLE binary file.

Questions :

1 - Is there an electrical risk to configure the 15kLE with the 10kLE file (IO configured in output instead of input for example) ?
2 - Is the FPGA partially programmed or the programmation is active only at the end when conf_done is OK ?

3 - Is there an other method to know to FPGA reference ?

Regards,

Jerome