Dune: Imperium · Board game rules
Are the effects in the gray box on Imperium Deck cards mandatory or optional?
Quick answer
Effects in the gray box (Acquire effects) are mandatory when you acquire the card, but other card effects with arrows are optional if they show a cost. [p.16 — Icon Guide and Additional Terms]
Details
Acquire effects appear in a special gray box underneath a card's cost and trigger automatically at the moment you acquire that card from the Imperium Row or Reserve. [p.11 — Acquiring Cards] These effects resolve immediately and cannot be skipped.
However, many other card effects use arrows to show a cost (left of the arrow) and an effect (right of the arrow). These are always optional: you are never forced to pay such a cost, though if you don't pay it, you won't gain the effect. [p.9 — Board Space Costs] This applies to effects on cards you play during Agent turns and Reveal turns.
The rulebook does not explicitly state whether Acquire effects themselves can be declined, but since they are presented as automatic triggers that occur "at the moment you acquire the card," they appear to be mandatory and not subject to the optional cost rule.