If you want to change Parker's properties without affecting all other "miner1" entities (Parker's entity type is "miner1"), you'll need to make a new entity class in entity.tbl with identical properties to the default "miner1" (call it "miner1AI" or something like that), and replace each instance of "miner1" with "miner1AI" in every .rfl in levels1-3.vpp which have "miner1" entities (there will be a lot).
The easiest way to do this is with the following steps, however I can't 100% confirm this won't mess up some scripting done in some specific levels. There will be a bit of trial-and-error involved.
1. Open .rfl in REDPF
2. Press Shift+W, Shift+Q, and Shift+H (to unhide and unlock everything in the map)
3. Tools->Select Objects
4. In the "Show In List" section of the "Select Objects" dialog, untick everything except "Entities"
5. Here's the somewhat tricky part. Most of your "miner1" entities will probably be named "miner1", however in some instance, I'm sure the level designer renamed them. It might take some trial-and-error to make sure you get them all.
6. When you have your group of "miner1" entities selected in the "Select Objects" screen (hold CTRL and click on them), press OK
7. Press Ctrl+P to open the properties dialog for your selected entities
8. Change "Class Name" from "miner1" to your custom "miner1AI" class and press OK
NOTE: If "Class Name" is blank as opposed to reading "miner1", you have entities of multiple different classes selected. In that case, I'd back out and ensure you only selected the entities you wanted. Otherwise, you might end up changing some of the guards, mercs, creatures, etc. into miners, which could mess up a lot of stuff.
For any additional "miner1" entities you may have missed (probably because the level designer set a unique script name), locate them in your map, click them, Ctrl+P to open properties, and set "Class Name" to "miner1AI" as above.
After you've done that and saved all the .rfls, pack them into a new .vpp (or multiple), and put the .vpp(s) in a folder under "RedFaction\mods\" (so if your mod is named "ParkerSpeed", your directory structure would be "RedFaction\mods\ParkerSpeed\"
You can then edit the miner1 entry in entity.tbl as you like, pack it into another .vpp file, and put that .vpp into the same "ParkerSpeed" directory under mods. Then, in the PFLauncher, select "ParkerSpeed" from the "Mod:" dropdown, and launch the game.
Red Faction loads .vpp(s) from the mod folder after loading the stock game content - meaning if levels1.vpp has a file named "L1S1.rfl", and you have a file named "L1S1.rfl" in a .vpp file in your mod's directory, the copy in your mod's directory will be the one loaded in-game when you start a new campaign.
Hope this helps! Let us know if you have any other questions or run into any trouble.