By RAW, no, because you don't have the Channel Energy class feature (you have the or Sealord or Natural Healing class feature, respectively.)
As a GM, I'd still say no, because Sealord and Natural Healing don't have any normal effect on undead, so I don't see why they'd gain one just by picking up Channel Smite.
I could see some GMs allowing it however, but only against undead versions of the creatures you're specifically allowed to heal.
To that, I would point out that SLAs work "like spells" but are not, in fact, spells.
Same argument I'd use here.
I am on topic, as it's a relevant comparison.
Maybe not the answer you're looking for, but valid none-the-less. ;)
SLAs are not relevant because channel energy and abilities granted by the terrain domains are both supernatural abilities and the wording in the sections treats them as identical except for the listed exemptions.
The only evidence I can see against the notion is that possible assertion that channel smite alters the effect as elemental channel. However if that is not assumed to be the case then I would think that it could work, dm permission necessary, but as stated above only against undead versions of what you could heal with it.
No this wouldn't work. The channeling granted by the Aquatic and Swamp domains doesn't let you harm anything- only heal or command. Channel Smite is all about doing damage. So Channel Smite would definitely constitute as "altering the ability," which is forbidden.
Now if the Aquatic domain had the option to heal water creatures or harm fire based creatures, then I could see allowing Channel Smite to add damage against fire creatures. But it doesn't, so it doesn't work.