It does appear you're correct. To use Saint-Andre's translation as a starting point:
VS71. Ask this question of every desire: what will happen to me if the object of desire is achieved, and what if not?
πρὸς πάσας τὰς ἐπιθυμίας προσακτέον τὸ ἐπερώτημα τοῦτο· τί μοι γενήσεται ἂν τελεσθῇ τὸ κατὰ τὴν ἐπιθυμίαν ἐπιζητούμενον; καὶ τί ἐὰν μὴ τελεσθῇ;
NOTE: Literally, τὸ κατὰ ἐπιθυμίαν ἐπιζητούμενον means something like "what is sought because of this desire" (cf. Aristotle's Nicomachean Ethics 1098b22); however "the object of desire" is more readable in modern English.
A more literal translation (sacrificing eloquence) would be:
Concerning all the desires, this question must be applied: What will happen to me if what is sought because of this desire should be fulfilled? and what if it is not fulfilled?
τελεσθῇ is a 3rd person Singular Aorist Subjunctive Passive verb. One page I found explains the aorist subjunctive as " if the subjunctive mood is used in a purpose or result clause, then the action should not be thought of as a possible result, but should be viewed as a definite outcome that will happen as a result of another stated action." That seems to apply here, since applying the accomplishment of the desire is a result of asking the question. It is also doing the action and asking "what will happen to me" if this action is completed. It seems to be the person is:
- Recognizing a desire in themselves
- Trying to imagine themselves in the future as having accomplished the action that fulfills the desire
- Imagining what will happen to them after that desire is fulfilled: Did the action fulfilling the desire bring pleasure or bring pain?
- Then acting in accordance with that future self's feeling of pleasure or pain.