This is a brief overview.
I would suggest starting by creating a folder to hold all your working files, with sub-folders as appropriate (here's an example)
Extract both the RIM files for the module in KTool under RIMs -> Modules.
Select unk_m41aa.rim and unk_m41aa_s.rim in turn and hit the "Extract Entire RIM File" button on the top right (I put them in the SOURCE folder in the above example)
Using the ERF/RIM Editor, create a new MOD file named unk_m41aa.mod
Select all the module's files you extracted in KTool, and drag them into the ERFEdit window, then save the MOD
Make a copy of the module's GIT file, m41aa.git
Open the GIT with K-GFF
Start by going to View -> Fold All, then expand the base STRUCT node to reveal the GIT's structure
Expand the CreatureList node
If you expand the first few STRUCTS, you'll see there are already three Gizka in this module using two ResRefs - unk41_gizka and unk41_gizka002
Checking those UTCs in KTool, we can see some important dev notes in the Comments tab, so we'll go with unk41_gizka
In K-GFF, right click on the first STRUCT and choose Copy STRUCT and then right click on the base CreatureList node, right click, and choose Paste STRUCT
A duplicate of that STRUCT will appear at the bottom of the list, which we can now edit as appropriate
Before proceeding further, you'll need some co-ordinates. You can generate these either via loading up the module layout in Max/GMax or by running around in-game with an armband that spits out co-ords of the player's position.
Edit your new entry in the GIT, changing the X/Y/ZPosition values as appropriate
You will see two values for rotation, XOrientation and YOrientation. These are the COS and SIN of the rotation in degrees, respectively. As these Gizka will be hopping around anyway, just leave the existing values.
Repeat with duplicating and editing the STRUCT for however many new Gizka you want to add. Save the GIT when done.
For testing purposes, you can just copy the MOD into your K1 modules folder, then open it with ERFEdit and drag and drop your edited GIT in. Save the MOD.
Start the game and load a save from before entering the Central Beach module for the first time.
Examine the quality of your handiwork.
You'll probably want to test various position tweaks. They take a little bit to start hopping, so probably don't put them right outside the Hawk's loading ramp.
Once you are happy, you can set up the mod with a TSLPatcher installer
Read the included PDF for instructions on how to create a TSLPatcher setup
The gist in this instance is you need to difference your edited GIT against the original and have it inject those changes into the MOD
Here's a basic setup so you can see how it works