Stop Co-GMing.

Clearly, there are at least two (and, it sounds like there may be three) competing ideas for what The Campaign should be. Since you've tried (and failed) to convince Tim that his "tweaks" and loot are making it impossible for you to run your sessions in the same campaign, stop sharing the campaign: his style and yours are simply incompatible (note: neither is necessarily "wrong" or "bad", just "different").

Depending on the desires of the rest of the group, there are two major options:

1. you can bow out gracefully ("I'm sorry, this isn't for me, but have fun!")
2. your group can rotate campaign worlds (and, perhaps, systems) instead of just GMs
   • on a regular cycle (weekly/monthly/...)
   • between "chapters"
   • between "campaigns"

I'm in a group that's rotated successfully for years, even with slightly different players (one person worked a rotating shift, so was only available "2 on, 2 off"; that helps); I've also had friends gracefully bow out without causing problems re-joining later when a new game/campaign was starting. I've also had friends who had a long-running "God-mode" campaign interspersed with "Krazy Kobold Adventureses", which acted as a palette cleanser between "chapters" (in that particular case, they were explicitly in the same world, but the Kobolds heard about fantastical things that were happening "way over there" and never directly affected them).

It appears that you already know how to generate tokens and assign them to player control.

As much as possible you can do this in advance - things that players have control of in their Journal, they can drag and drop onto the screen. For example, I have a player who frequently casts spiritual weapon. I make sure I have an appropriate token for her in the journal before the game starts, and she can drag it to the board when cast. You can similarly make sheets in advance for creatures they might summon with a conjuration spell, or transform into using the druid's Wild Shape feature or one of the polymorph-type spells.

However, for truly on the fly player-creation of tokens, I don't think there is Roll20 support. One possible workaround would be to enable the players as co-DMs on the game, but require them to sign in as players for play sessions. If you wanted them to create or modify a token, you could have them log out, log back in again as a DM, do the work, log out, and then log back in as a player. In one game I DM, I have a player who occasionally acts as my assistant. I ask him to follow that procedure when I need some tokens or terrain put on the board, or a macro written or edited, while I attend to something else. Provided he is not in the middle of his own turn, it is reasonably seamless.

Of course, this workaround assumes that you have players you can trust to not look at things they should not have player knowledge of (unrevealed areas of the map, NPC stats, GM text on handouts, etc.), since having DM powers means they can log in as a DM even when you are not present. In that case, a slightly different workaround is to give them GM powers in one game, so that they can create tokens / characters there, and when you have a chance you can move them to the game in which they are a player. Note that you can have two different games open at the same time. This way they can make the new token when it is not their turn, but you still have to move it over when you have a chance as a DM. Once it is in the game, they can drag it to the board.