Alright, let's see if I can figure this out...
First you need to open up blueprint.txt (in scripts/server) and find the blueprint of a unique or set piece you want to edit. I don't know all the item ID's but luckily most items have names, even if many are in German or just have a fragment of the name. If you can tell me what items you might want to edit, I can probably help you find the blueprint ID. I don't know what your character has, so I'm just picking a random one, the unique ring Nyarlathotep's Creeping Madness. The blueprint looks like this:
newBlueprint = { id = 2541, name = "unique_ring_Nyarlathotep", palettebits = "1111111111111111", dmgvariation = 0, minconstraints = {20,14,0}, lvljump = 20, usability = 0, allotment_pmfpi = {1000,0,0,0,0}, uniquename = "unique", specialuseonly = 0, bonusgroup0 = {543,700,1,9,0}, bonusgroup1 = {886,750,1,9,0},
bonusgroup2 = {871,500,1,9,0}, itemtypes = {7152,}, wearergroups = {'WEARGROUP_DEFAULT',}, } mgr.createBlueprint(2541, newBlueprint);
The bonuses (item modifiers) are the lines that say "bonusgroup0" for example. The is where you'd add the Survival Bonus modifier. The ID of Survival Bonus is "871". So as you can see in yellow I have added a new bonus to give the item this property. Maintain the numerical order, for example if the bonuses go up to bonusgroup2, then make sure the next one you add is bonusgroup3. I think there is a max of 5 bonuses (so the highest allowed would be bonusgroup4), so you'll have to pick an item that has less than 5 bonuses or else you'll have to replace an existing bonus.
I copied the values from another item that has Survival Bonus (Officer's Saber), but I think increasing the second number in the sequence (500 in this case) should give you higher amount of Survival Bonus. I think 500=5.0%, so I might try 9000 to bring it up to 90%.