I am sure it has been tried with little success...Palma requires a specific bullet weight, and velocity is everything. Virtually all palma rifles have a long barrel in the ball park of 30" or more. (Sight radius is also part of the package). The SSG69 "can" propel palma bullets to 1000yds, but they are barely supersonic at that range...Depending on the load may not even be. You would be at a major disadvantage if you are trying to win. If you are dead set on using the SSG as a palma gun, my advice is to find a SSGp4 and re-barrel it. (They are the only SSG69 series threaded). SSG69 stocks are not really adequate for palma use either.
Personally, I think the SSG69 could have been the best 308 in it's class, if Steyr had made any attempt to modernize it or improve on it's faults.
Instead they have gone to the cheaper to mfg SBS series.
Bottom line, you "can" shoot a stock SSG69 as a palma rifle, but dont expect to win.
I used to own an SSG 69 with a 26 inch barrel, and now own a .308 SBS. They are both great shooting rifles. The SSG ( Model L ) action is still made. It is so cool, so smooth.
I have just started trying Palma bullets in some of my really accurate .308s - Sauer 200, SHR 970, and SBS Prohunter.
My first load which shoots 0.5 inches in all 3 of them is 43.6 gr Varget with a Federal 210M primer and a Sierra 155-gr Palma bullet.
To seriously shoot competition, you need two identical rifles, bringing one along as you wear out one and rebarrel it. The SSG is good for 20,000 rounds if you don't overheat it. It was not meant for competition. It was meant as a military sniper rifle. Use it for that and hunting, enjoy it, keep it forever. If you want to dip into Palma, you need a screw in barrel, about 30 inches long.
The SSG 04 & SSG 08 both have threaded barrels, the 69 (which they discontinued this year) has a pressed Barrell which can really only be changed by Steyr. The biggest challenge is going to be your barrel. A 1/12 twist will definitely be transonic at 1000 yards but a 1/10 will make it fine. I shoot my SSG 08 at 1250 yards with Lapua 155 Scenars (moly) and it shoots great (1/4 MOA). Like sling says, Palma might not be the best home for your SSG but they soar in tactical precision matches as they work exceptionally well in challenging environments where those customs are way too finicky. Find out which twist you have and that should tell you more about its long-distance capabilities. Some have 1/12 and some have 1/10 twists.