I want increase my carrying limit in Morrowind without modifying any stats that affect other things (like Strength).
For a permanent change, you can use the construction set to change the setting
(click new plugin, no need to load the .esm, -> gameplay menu at top -> Game settings -> scroll down to fEncumbranceStrMult click it and change the value in the box on the right -> save your plugin and check its box in the game launcher.)
Which is a float that multiplies your strength to give your max encumbrance. Default value is 5, meaning 5*str=encumbrance. Change it to, say, 10 to have double encumbrance.
There is no direct way to modify the encumbrance trough the console in Morrowind. Encumbrance is directly calculated from strength, and, aside from spell effect, nothing else modify it.
Otherwise, you could add yourself a bunch of Feather potions (
p_feather_e) or scrolls (
sc_ulmjuicedasfeather), and use them when you need to bypass the limit.
I found you can overflow the encumberance by carrying too much
find a shopkeeper whom when you buy some two ingredients, like restore fatigue or something, they don't go away like if you buy 5, they keep 5). Mages Guild is good for this
have a decent alchemy skill, it's not that hard if you have a pestle, money, and patience.
every time you sell ingredients back the shopkeeper will get double, this is an easy way to buy like 400 ingredients to alchemize at once for money. Strangely, I found once I got those ingredients, I made the potions, then when I sold them, my encumbrance went down into negatives, and stayed at 0, even when I dropped something and picked it back up.
I think there's something to do with an overflow, where when it's over 1000 it brings it down to 0, though I don't think it properly handles negatives, so it keeps the negative intact, i.e. 350 - 800 = -550, but it doesn't actually bring it up to 0, just displays it as 0, so you can still go back up over 1000, but every time it will decrease your REAL encumbrance by however much overflow you sell.