I've got no idea what was in the service bulletin about the bridged capacitors... But mixing the ceramic with the electrolytic does change things. Total capacitance goes up (c Total = c1 + c2) Frequency response changes slightly since the devices have different characteristics (ESR - equivalent series resistance differs) Also they behave differently for reverse voltage.
I wouldn't be surprised if the original design either should have had a higher capacitor value or required two different types for frequency response characteristics.
Bridging them was definitely a low cost modification that didn't add to much to the manufacturing process.
It's been a long time since I've thought about hardware design at that level! Kind of fun to see this since I doubt modern hardware sees many changes like this.
Good luck with the journey!