Here is the way i do them :

Use S_king app , to make a correct opening_plugin for 3.52 ,padded sound and file size respected.

Open your favourite hex editor, and select for the 3.5x one - 0x000042A4 to 0x00010384 - then copy it.

Next open the 3.71 opening in the Hex editor and  select range - 0x00003D94 to 0x0000FE74 - and insert your previous copied range in to the 3.71 one.

Save - that's it now you have a working coldboot sound for the new firmware.