Claire Classic Outfit and weapons Claire gets

There is no need for a mod. If you complete a Hardcore run on any scenario (1st or 2nd) with Claire, you unlock the Classic Costume Custom set, among which you can choose her Classic-without-jacket attire at will.

A mod will end being more of a hassle than simply using Game Trainers or Cheat Engine that makes you invincible, give you infinite ammos and so on to complete Hardcore... Or eventual tools made on here.

Cheat Engine is also your friend, it currently allows you to replace inventory items with those of your choice and that include shotgun and stuff. It's a little bit glitchy but it's a WiP.

also how does the cheatengine thing work? is there like a tutorial

1. Download Cheat Engine. Download link and install it.

2. Download RE2.CT on the link I gave you. It should be available at the bottom of the first post under download. Take the one right under Latest. But just in case, Direct link This is a "cheat table". Basically it comes with premade cheat options that the author of the table made. The options are shortcut to hex editing, just like a trainer but more versatile.

3. Launch RE2.CT. Cheat Engine will automatically open with the table.

4. Launch the game.

5. Alt tab/minimize the game and return to the RE2.CT window. You should see an icon flashing green on the top left corner of RE2.CT's interface. It's the icon of a computer with a lens. Click there, then select Resident Evil 2 in the process list.

6. And you're done! Now you just need to click on Enable in blue on the big white space of RE2.CT's window, which will activate the possibility to choose the options of your choice. From there, activate options at your leisure. Undead, no reload, etc.

7. To replace weapons or key items, you need to activate "Highlighted item (no aobscan)". From now on, the latest item that was highlighted in your inventory with your mouse will be registered for replacement, you will see it named next to Item Id or Weapon Id. If you double click directly on the item's name on RE2.CT's interface, you will see a dropdown menu list tasking you to change the value.  You change like that. It's very important that if you switch from a key item to a weapon and vice versa to determine which kind of item it is (a weapon or not).

It's a lot to process, but since you're asking for a mod for something that is already available by default in it, I think it's normal for you to work for it a little bit

Finally: items you replace are exclusive to your inventory, so it won't affect the items you'll find. If you want shotgun shells, you'll have to replace an item for them.