Can I trigger only some of the (enabled) content plugins in my fields ?

Yes you can,
FLEXIcontent overrides Content Plugin Triggering, and thus can trigger content plugins selectively

BENEFITS of FLEXIcontent Selective plugin triggering:

1. better performance than triggering ALL enabled content plugins, since you may only need to trigger only specific content plugin(s) in some of your field
2. you may avoid some unwanted replacements or side effects if all content plugins are triggered in your field

-- normally joomla content plugin triggering, will trigger ALL content plugins that have been loaded up to the point of calling

e.g. if we used normal joomla content plugin triggering when triggering plugins on the contents of FLEXIcontent fields, then the following scenario describes what will happen:

    FLEXIcontent  field1  triggers  plgA and plgB
    FLEXIcontent  field2  tries to trigger only plgC,
    -- but it will actually trigger ALL plgA, plgB and plgC,
    -- this because field1 has already loaded content plugins:
    plgA and plgB

with FLEXIcontent selective Content plugin trigger method,
the field2 will only trigger content plugin plgC

Other information:

-- For items, these Content Plugin events are ALWAYS triggered (on their description)

1. onContentAfterTitle
2. onContentBeforeDisplay
3. onAfterDisplayContent

-- For each field, the content plugin event:

1. onContentPrepare
   is triggered OPTIONALLY via the (XML file) parameters:

• trigger_onprepare_content
  (effects both item view and category view)
• trigger_plgs_incatview
  (if this exists it is used in category view instead of above)