Blocking Modifiers Crafting Help

So I have conflicting information from two reliable sources as to how exactly blocking modifiers from appearing during a craft actually works in practice.

For example, if I am trying to unveil a specific suffix (4 sec trigger wand) using veiled chaos, can I craft things onto the wand before I unveil that can block other unwanted outcomes from appearing?

I understand that there are tags like "attack" etc, if I craft an affix with an "attack" tag, does that "block" other attacks from rolling or unveiling, or lower the chances of those types of mods from rolling/unveil?

Or I have also heard about "mod groups", do those play a role here?

Thanks!

You may want to check mod groups on PoE wiki or craftofexile. While there is no way (I know of ?) to directly compute the odds to roll a specific mod with veiled chaos/aisling, craftofexile provides the weight and mod group of each possible mod.

When you craft a mod (or have this mod rolled), no other mod within the same mod group can be rolled or crafted.
So in your situation, ie wanting to roll the 4s trigger suffix mod, you want to get a veiled suffix + empty suffix, then craft the mod that will block the most weighted mod group; and only then you unveil, as no mod of this group can appear.

In this case, and unless I'm mistaken, best mods to block are DoT multipliers, as one will block all (phys, chaos, cold, fire), removing a 4000-weighted mod group.

Super informative, thank you so much for your detailed and well-explained replies!