Each cell in an AGM battery will have it's electrolyte sealed within it's own cell casing. Having said that, I can't tell you where the boundaries of the electrolyte chamber are, or how the internal strapping that connects the cells is configured. It might be possible to cut the plastic casing apart, incise around the interconnecting strap, and butterfly the battery without ever rupturing a cell, but I have no idea the issues involved. At worst, you would have to find a way to cut and then expose the interconnect between the cells at the end of the row. If the interconnects are made of lead, a good battery shop could probably cast you some new terminals with little effort.
Remember that an Optima is going to have a gelled electrolyte, so it's doubtful that it would "spray", but you would obviously need to exercise caution while working on it.
My suggestion is to see of you can find a dead Optima red-top (lots of them around, look in wrecking yards) and experiment on that first, it's probably an identical design to the yellow-top. Have lots of baking soda and water around, and wear lots of protective clothing! If you discharge the battery completely first, the electrolyte will be more water than acid.
Have you considered contacting Optima and seeing if batteries are available in a three-pack configuration? There must be at least some demand for 6 volt yellow-tops.
Remember that an Optima is going to have a gelled electrolyte, so it's doubtful that it would "spray", but you would obviously need to exercise caution while working on it.
My suggestion is to see of you can find a dead Optima red-top (lots of them around, look in wrecking yards) and experiment on that first, it's probably an identical design to the yellow-top. Have lots of baking soda and water around, and wear lots of protective clothing! If you discharge the battery completely first, the electrolyte will be more water than acid.
Have you considered contacting Optima and seeing if batteries are available in a three-pack configuration? There must be at least some demand for 6 volt yellow-tops.