DVD ISO file hash does not match

[mpcfun]

If I use something like UltraISO to create a new "UDF DVD image" or "DVD-Video image" (what's the difference?)
and copy a DVD ISO's folders contents into it and give it the same iso file name (volume name?)
I still can't get the new ISO to match the file hash of the original DVD ISO file.
Is the ISO metadata being altered?

How can I edit the ISO metadata so that the new and old ISO are completely identical?
It doesn't have to be UltraISO, that's just what I tried doing it with.

[Vidd]

Did you check the file date/time stamps? That would create a different hash.

But it is to be expected that different programs create different ISO files. While they should all be according to spec, some ISO programs will optimize the disc layout for optical disc reading. This is especially true of a professionally authored dual layer DVD video discs.

I don't understand what you are trying to do. If you have the original ISO and are trying create an ISO with the same hash, why create a new file when you can just copy the original? Any edit you make to it will change the hash.

[mpcfun]

When I mount the new ISO and old ISO, the files inside match the old created and modified dates as in the original. Also same file hashes.
Just not the ISO itself.

I'm trying to preserve the exact original contents or at least understand what metadata is being changed and change it back.

An example use case is saving hard drive space by deleting DVD ISO files but first burning them to physical discs
and adding extra stuff (why waste the extra space if it's there on the disc, luckily it doesn't affect DVD playback ).
Then later, if I want to create an ISO file of the burned disc, I can remove the extra stuff
with UltraISO (or whatever program) so that it's just like the original DVD ISO, including matching the file hash.
The contents (.VOB, .IFO, .BUP, folder names, etc.) are apparently identical but not in ISO form which may contain metadata that doesn't match the original.

Also, if I decided to only preserve the contents (e.g. VIDEO_TS folder) instead of the entire ISO,
is that a bad idea? If I burn the folders (and use the same .iso file name, if that matters?), will it affect DVD playback?