Old tags, pre 0.15:
},
"shadowmobs.grue": {
"Type-Enabled": "MONSTER-true",
"Tags": "{spawn:light,5,15:maxSpawnHeight,40}"
}

became this at conversion:

},
"shadowmobs.grue": {
"Type-Enabled": "MONSTER-true",
"Spawn Operand": "OR",
"Spawn Tag": "lgcy.light(5,15)||lgcy.height(40,256)",
"Despawn Tags": "lgcy.light(7,15)||lgcy.height(40,256)",
"Contents": []
}

Is the addition of the Despawn tags here intentional? Or necessary? There are no conditions under which I would like the Grue to NOT despawn

-apologies, I should have included a different example, since the Grue's tags did not convert exactly as I've indicated above anyway (the min height was converted as args[0]).

Below is the unedited converted entry for another entity that had Spawn tags previously, but no despawn tags.

Old tags, pre 0.15:
"LIVING_HANDLERS": {
"arcticmobs.arix": {
"Type-Enabled": "MONSTER-true",
"Tags": "{!spawn:sky:&light,0,6}"
},

became this at conversion:

"LIVING_HANDLERS": {
"arcticmobs.arix": {
"Type-Enabled": "MONSTER-true",
"Spawn Operand": "OR",
"Spawn Tag": "!(sky()&&lgcy.light(0,6))",
"Despawn Tags": "!(sky()&&lgcy.light(0,6))",
"Contents": [
"arcticmobs.arix"
]
},

I hope that does a better job of explaining my question.

Is the addition of the Despawn tags here intentional? Or necessary? There are no conditions under which I would like the Grue to NOT despawn

It is neither intentional or neccesary and can be deleted. Will investigate when I return home, as well as actually uploading the correct versions of files.

:) ta. Safe journey

Deleting the respawn tags (the entire line) results in them being re-added.

Yes. It would this line is clearly incorrect: https://github.com/ProjectZulu/JustAnotherSpawner/blob/master/src/main/java/jas/common/spawner/creature/handler/LivingHandlerSaveObject.java#L216
referencing String spawnTag param instead of String despawnTag.

Should (edit: though not intentionally of course) happen to every entity on reloading a 2.0 entitysettings file

Should be fixed let me know if it persists.