What is the ruling when a traveler who intended to shorten the prayer (Qasr) subsequently intends to complete the prayer (Itmam)?

Primary text

If a traveler intends to complete the prayer (Itmam) after initially intending Qasr, or intends an action that necessitates completion, such as making the intention to reside (Iqama), or changes the intention of the journey to one of disobedience, or intends to abandon the journey, and the distance of return does not permit shortening the prayer, the traveler is obligated to complete the prayer. Those praying behind such an individual must follow this completion. This is the view held by Al-Shafi'i. The evidence supports this because the intention for the prayer of that time period, which is four rak'ahs, was established. The concession to reduce it to two rak'ahs was merely permitted. When the intention for the concession is dropped, the prayer is valid with the intention for the full amount. Furthermore, completion is the default state; shortening is only permitted under a condition. When the condition for shortening ceases, the default (completion) reverts.