how to select what to clean using cleanseFollow

Im not sure of the mechanic, but there is no way to distinguish between which poison you wish to cleanse.

The addon Decursive allows for some customization and prioritization for cleansing (from the description of the addon at Curse.com):

-Easily Filter out afflictions you don't want to cure or that are useless to remove by class (some are pre-configured).
(Such as afflictions affecting mana on non-mana classes, etc...).
-Choose between what you can dispel (magic, curses, poison, diseases, charms) choosing their priority. (this allows you to share the cleansing work with other players effectively)
-Prioritize or exclude members. (keep players, classes, or raid groups in a specific order to cleanse them in order of importance)

Also the addon Grid offers much customization for pretty much all casting as well as other items. It can be coupled with other addons/plugins to customize your UI.

This isn't what the OP wanted though--he was looking for a way to literally avoid ever dispelling something he didn't want to. From what I can tell, this addon does two things.

1. It stops your dispell macro (the one it provides) from working if the opponent has something up you don't want to hit. For example, it will keep you from using cleanse if Unstable Affliction is there, since cleanse might remove it.

2. If your class has multiple abilities that dispell, the macro will choose the one best suited based on your specifications.

For example, you have cleanse and purify to remove debuffs. Cleanse is 1 P, 1 D and 1 M. Purify is 1 D and 1 P. So, like an above poster said, it would be safe to use on someone with UA up. So the macro would check if they had UA up, and immediately disregard Cleanse. It would also see if they had a poison or disease up. If they did (and you had no other conditionals), it would use Purify. If they did not, it would do nothing.

You would never be able to remove a magic effect from the target when using this addon, unless you chose to manually. And then you still run the risk of activating UA.

The addon is undoubtedly useful, but still not what the OP wanted.

But I do want to personally thank you for that find, because it'll be incredibly useful if I ever PvP on a healer. :P

It's actually pretty good if you're holy, since you can keep sacred cleansing up a lot by repeatedly removing stacks of deadly poison. Gives a 30% chance for any magical attack or effect, or any poison or disease to completely miss you.

Same principle works for frost mages and winter's chill. If you cleanse just enough to keep sacred cleansing active a lot of attacks and cc will just miss you.