A cool combat use: 

"Disguise Self (1 hour, no concentration requirement) to look like a Medusa for an hour. Intelligent enemies will likely avert their gaze, granting you advantage on your attack rolls/disadvantage to their attack rolls against you."

Source: https://www.enworld.org/threads/spell-combos-under-concentration-economy.427645/page-2

Another combat use: 

Disguise Self/Seeming to deny an enemy's ability to differentiate targets based on visual cues (make everyone look like the same person, maybe?). Doesn't even take Concentration. 

During the 1-hour duration, can the spellcaster change the appearance of the illusion? Or, is it set once at the time of casting and unable to be changed so long as the original casting lasts?

Quote from Deecely >>

During the 1-hour duration, can the spellcaster change the appearance of the illusion? Or, is it set once at the time of casting and unable to be changed so long as the original casting lasts?

 Spells that allow that will say so in the description, so no.

I am very confused...
On my character sheet (Ranger - Gloom Stalker), it says I can cast this spell with higher spellslots... But I can find no benefit for doing so on this.
Can anyone help me out on this? Wth is DnDBeyond going on about?

I guess this is for if you run out of lower level spell slots then you can still cast it?

probably, in most cases that's the best outcome, mix this with silent illusion, voice of the chain master and you have your own version of mislead

probably, in most cases that's the best outcome, mix this with silent illusion, voice of the chain master and you have your own version of mislead

The eldritch invocation that gives warlocks the ability to cast this at will, while certainly having a lot of practical uses, also presents some fun cosmetic/roleplay uses. Taking a spell like this and allowing unlimited uses is always very fun, since it means you can use it for small, frivolous things without needing to worry about saving it for the right time.

Like, a fashion savvy warlock could use this to alter their clothes or give the appearance of makeup where there isn't any. Maybe they don't like the look of leather armor, so they use this spell to give the appearance of some stylish robes or something without losing the bonus to AC the armor gives.

You could be a kind of "casual shapeshifter," similar to the changelings from Eberron, though slightly different since this is just an illusion and changelings can't effect their clothes. I just really like things that allow for creative character building and small cosmetic decisions.

I mean I'd rule it as so. kinda up to your DM

Can you refresh the spell by casting it again before it ends?

If I used disguised self to create a top hat, would I be able to take off and hold onto the top hat or would my hand also pass through the illusion?

I think it goes with synerge - as with actor you change the way you move or speak as well. It makes your disguises harder to spot, as the difference within between the wished appearance and the masquarade will be covered by tzhe spell, but if someone bump into you, your costume would still be more or less the same, therefor less suspicious. You can add parts of your masquarade, for you doesn't have the right material, as make your weapon looks like a famous artifact or the item, what the guards search for the whole city looks like a mundane one instead... But the final words would always belongs to the DM, what he let pass, and what is inevitable. Maybe the only thing, what you get by this, is just an advantage on the check.

I would consider a Medusa an abuse of the spell, because of the phrasing ‘same basic arrangement of limbs.’  A Medusa has no legs, but a snake’s tail, and has many snake heads coming out of her head. I’d consider that a significant change to the arrangement of limbs . However what you are attempting to do with this IS specifically allowed with the 2nd level spell, alter self. 

It states you cannot change your body type, so not a different quantity of limbs. Does this mean that if you are an aarakocra (2 legs + 2 arms + 2 wings = 6 limbs) you could make yourself a centaur (4 legs + 2 arms = 6 limbs) with disguise self?

yes if the dm allows

Quote from Dangerdane >>

I would consider a Medusa an abuse of the spell, because of the phrasing ‘same basic arrangement of limbs.’  A Medusa has no legs, but a snake’s tail, and has many snake heads coming out of her head. I’d consider that a significant change to the arrangement of limbs . However what you are attempting to do with this IS specifically allowed with the 2nd level spell, alter self. 

 Medusas only have a snake tail in Theros. Also the snake hair isn't really extra limbs. (Atleast I wouldn't consider it extra limbs).

AY! DnDbeyond! This is also a gloom stalker spell!

Is there any spell that allows me to know if a creature has any loved ones who are dead? I want to use them together

Quote from ZeldinAlderlead >>

Is there any spell that allows me to know if a creature has any loved ones who are dead? I want to use them together

 Detect Thoughts