I don't like to unnecessarily create terminology, but these are key to my iteration methodology, and I recommend thinking in these terms:
Low-level changes: These are changes to individual cards or components.
Medium-level changes: Creation of a new rule or concept, or a small change to how a core game mechanic works.
High-level changes: Addition/removal/significant alteration of a core game mechanic.
Making a high-level change to your game will have a ripple effect, and necessitate many lower-level changes.
Your earlier iterations will involve higher-level changes to the game, while your later changes will almost all be low-level changes. Your game isn't complete if you've recently made medium or higher-level changes.
Whenever you make significant changes to your game, also pare its content back to the absolute minimum. You want to test those changes in isolation, and more changes are probably coming. You don't want to have to update all your content each time.
My gangster game underwent a fairly high-level change around revision #260. I removed 40 of the game's 65 locations, and all its 23 unique player power cards. I added them back in later, once the changes settled down.
Only change one mid-level thing at a time. Your game is like a roof. It has an interlinked structure. You can replace one timber at a time, but if you replace more than one, it can all easily fall apart. After a playtest, you may see multiple things wrong with the game, or want to go in a new direction. Resist the urge to change it all at once. You might either be forced to go back to a previous version, or you'll forge ahead, and become lost.
Just change the most important thing, and tolerate the rest in the meantime.
Sometimes, underwhelming things will stay in your game for quite a while. A single change allows you to test the change in isolation.
You don't have to fix everything at once, anyway. Some nagging problems will fix themselves, or be obsoleted by larger changes to the game. Just leave them there, and be aware of them.
These days, my approach is that making a high-level change is actually the beginning of a new game. You're fundamentally changing your core, which is the game. This change ripples so much that you effectively go back to the beginning of design, because everything else has to change. As such, I generally don't make high-level changes to my games. I either pursue the game as it is, or I abandon it. If I return to it, I actually do start again.
The recent occasions when I've made high-level changes to a game have either been erroneous, or high-level changes that are confined to that system. These changes maintain the function of that system, so it doesn't ripple, and disrupt the rest of the game.
A redesign is a return to the beginning of design, by reappraising high-level choices.
Many of the people I see endlessly working on the same game have, in reality, been working on a series of related games, and constantly restarting their design.
You should acknowledge when you're doing a redesign, because there's a good chance it's time to abandon the game, rather than restart its design.
Sometimes, I have a great idea, but I can't get it to work. I abandon the game. The idea rattles around in my head for a long time, and I eventually come back to it. My personal experience of redesigns has been very poor. It might be different with you, but I strongly advise against redesigning. A good idea doesn't necessarily become a good game, and the redesigns often fall into the same pitfalls as the original. Just come up with a new idea.