Which improvements can be added to Fiery/Icy Dragonsword?

I'm still kinda new. I want to understand how these swords work.

I understand that the hilt can't be changed. I think that they all come with a nice inscription (+15% damage when health > 50%). Can a pommel be added? Are these of gold rarity? How much do they go for?

Pommels can be added to any icy/fiery/vampiric dragon sword no matter what. Inscriptions however, must have the word Inscription in the description to be able to be modded. That means Icy Dragon Swords from the traveler gifts, not prophecies, and Fiery Dragon Swords from Nightfall. Vampiric swords only come from Nicholas the Traveler, so you don't need to worry about whether they come with an inscription slot or not.

http://wiki.guildwars.com/wiki/Sword_Pommel

Here's a list of the pommels available straight from the wiki.

The icy Dragon Sword from prophecies is the only of the dragon swords to actually come with an inscription already in place, and it is also one which cannot be removed. The icy dragon sword from prophecies that drops from the ice imps can also have its hilt dyed (and is blue rarity I believe), and the icy dragon sword from Nicholas is gold rarity, has an empty inscription slot (so no inherent 15>50), but you cannot dye the hilt a different color.

Fiery dragon swords can only be gotten as loot, so they come in blue, purple, and gold rarities. The hilt on FDS's can be dyed, and if found in Nightfall as loot can also be inscribable.

There is also a Vampiric Dragon Sword to be gotten from Nicholas the Traveler (and ONLY Nicholas), which, like the FDS and IDS, has a vampiric hilt that is NOT changeable, although it is inscribable and of gold rarity. Its hilt cannot be dyed.

That pretty much covers it lol.

I had a icy dragon sword from one of these imps, it was gold, and 15^50 and icy ofc^^

these were changed from blue rarity to gold rarity in an update two years ago.