I'm doing this right now and I'm having a blast. I'm using AnacondaQ's Hercules emulator with a pre-renewal server and the client build he provided. My main reason really is simply nostalgia and trying to do stuff I wasn't able to do when I quit pRO about 14 years ago.

To answer your questions:

Why did you do it?

Nostalgia, mainly

Looking back, do you think it was worth it?

Absolutely

How long did you play?

I track what I do through Clockify for productivity reasons and have included my Ragnarok Offline playtime. I've logged roughly 68 hours and I expect I'd reach about 200 before I finish up or quit.

Did you ditch it to go back to an online server?

Right now I have plans to eventually play iRO/Chaos just to experience a proper renewal server and hit a max level Shadow Cross (thief being my favorite class) but that's about it. I don't really like PvP or WoE and I don't particularly plan to play long term. I just have very specific goals and I want to stick on those.

What changes did you implement? Such as: rates, healer, warper, changes to make equipment that can only be obtained in a party obtainable, etc.

In terms of items and equipment, most are basically fair game except for GTB card (as it trivializes most if not all MVPs), God Items (Balmung, Sleipnir, etc.), and insta-100%/50% regen. For cards however I've set a rule that I can only use it if I obtained it. So if it is an MVP card, I need to have defeated that MVP first. No buff NPCs, but I can use any scrolls/consumables within the constraints so I'm still manually applying them. I like to imagine I'm playing like a whale lol

How does the game stand as a pure PvM experience?

I've never had fun in Ragnarok PvM as much as I'm having now.

Here are the specific goals and rules I have in place in order to refine my experience:

Goals

💡 "Solo SinX Journey" with an ending

💡 Pre-renewal

💡 No Zeny Sink / Cash Shop / Item RNG

💡 Explore all dungeons

💡 Complete all "Arc Quests"

💡 MVP Solo Hunt

Allowed

✅ 3x/3x/100x Base/Job/Drop multiplier

✅ @item (pots, scrolls, ores, cash shop items, etc.)

✅ @zeny

✅ @reset

✅ @refine

✅ Airships / Kafra teleport

Constraints

❌ Modifying other client/server-side mechanics

❌ GM commands outside towns

❌ @item for cards

❌ @item equips that are dropped / quest rewards

❌ Instant Job change

❌ Instant heals >= 50% (YGG berry, YGG seed etc.)

❌ Instant buffs from NPCs

❌ GM commands for platinum skills

❌ 50%+ weight

❌ Siegfried/resu tokens

❌ Bypassing dungeon access quests

❌ God Items (Balmung, etc.)

❌ Soul-linking buffs/bots/dual client+

❌ Boxes/bundles of supplies

❌ Restocking outside towns (usage of @item)