UGE - Universal Game Editor
This is a 1990s game editor that allows hex-editing of most save game files, but not all. You must be able to decrypt the save game files, which is not always possible for amateurs. (It is abandonware...)

It works in decimal numbering, handy when hexadecimal is not your forte.
You create Module, mdl, files that name and list the possible alterations. (Alternately, you may find the mdl files on the internet.)
Lst files are text files that give names and definitions for each variable in a given mdl file.

UGE won't run natively on Windows 10, but DosBox will run UGE normally.

(Create a folder called OldGames and put the UGE folder there. I assume the use of UGE10 for the UGE folder name.)
If you exited out of UGE, DosBox is still running and you want to restart UGE, just type UGE and hit Enter.

For an understanding of UGE, see the "UGE - FRUA Hacking" topic:
http://ua.reonis.com/index.php?topic=2404.0

For a copy of UGE, see:
http://frua.rosedragon.org/pc/misc/uge10.zip

There is currently no module for any of the Ishar games. Modules could be easily created, hopefully.

UGE is generally useful for any game that does not have its own editor...

I am getting somewhere with decrypting. Ishar 2 has a lot of features that I have not seen before.
There are no individual PC records. Rather, all information is stored in 5x1 or 10x1 arrays.
Cont1.fic is the map for Irvan's Island, it has a length of 60 Bytes. It is transposed when read in a hex editor, x=y and y=x. It has two sections (a) the terrain and (b) the special events that happen on certain squares.
Information about PC money seems to be stored in at least two places.
Inventory slots seem to work like this:
3 6 9
2 5 8
1 4 7

It is big-endian, which format is normally used by Mac, unlike Windows.

Variables may be listed one way on the screen, then they are listed another way in save game file.

Useful function on the Command Prompt, File Compare:
FC /B QUINCUNA.SAV QUINCUNB.SAV
Greenshot is handy for making quick screen captures of interesting information

Spreadsheet below shows progress to date:
https://www.freewebs.com/ishadnha/Ishar2.zip

WOW, nice progress. :)
BTW, the whole game was actually created on the Atari ST or FALCON ( Don't remember now which one ). The engine it self allowed to be afterwards to be the game compiled for any type of OS ( AMIGA, ATARI or MSDOS ). The file structure should be almost the same, just the AMIGA and ST version have the better sound effects.

Thanks for the already founded info, it's nice to learn more about this game. :)
Holding you the fingers with the next progress. :)

It sure is different, I am used to working with Windows programs...

En1.fic is a file that stores a lot of the information about NPCs. Typically it is stored in sequences of 110 Bytes. There is provision for 110 NPCs, this includes hostile monsters as well as recruitable NPCs. If the variables are recorded as two-Byte then the sequence will occupy 220 bytes instead.
A lot of the same sequences also occur in the sav save files. Party has only 5 members but the file has information for all NPCs.
I am drawing up a table to show all data for all recruitable NPCs. Lack data for Grimzel and Grimz. A new version of the spreadsheet has been uploaded.

986: PC# XP in Hundreds, 2 Bytes per PC.

3481: Starting Money (Thousands and up)
3701: Starting money (H,T,U)

1006, PC# Unclear
1016, PC# Maximum Vitality
1026, current PC# Money Hundreds, Tens, Units
1006 sequence should be current PC money, Thousands+

Still can't fully understand changing location... Teleporting by change of coordinates, where you arrive is a mess. It seems the business is more complex than altering two numbers.
You need to wander away from your destination, for a while until scenery returns to normal. Coordinates for x and y are only part of the story...

I have uploaded a new version of the spreadsheet, see the link at the bottom of post #2.

"It is big-endian, which format is normally used by Mac, unlike Windows."
This is only a problem when the given variable is two-Byte. Getting around this problem, there are several possible approaches to altering Ishar 2 saves:
Use the module, especially its Lst file as a guide to hex-editing with an ordinary hex editor.
Use an Excel spreadsheet to handle the editing.
Use what I call inverted decimal numbers to make 2-Byte numbers work with the UGE. Big-endian numbers will be read as little-endian.

Treat each number in a 2-Byte variable as a number variable in its own right.
(For items that are always preceded by a set 255, this is easy.)
Idea is that you know how big an increase you want in the variable, so it is easy to see if you want to alter the left variable, the right variable or both. Left byte is a multiple of 256 while the right byte is in the range 1 through 255.

Latest version of the Ishar 2 module has been uploaded.
Ishar 2 Quick Notes.txt has some words "not seen before." This should read as "Ishar 2 has a lot of features that I have not seen before."

It looks like the other three Ishar games may have a similar structure. If so, it will be easy to draw up mdl module files for them.

I uploaded an Ishar 1 module, for link see:
https://www.freewebs.com/ishadnha/Ishar1.zip