To increase SSD capacity, high bit-density cells, such as Triple-Level Cell (TLC), are utilized within 3D SSDs. However, due to the inferior performance of TLC, SLC/TLC hybrid 3D SSD is designed to use a portion of the TLC space as an SLC cache to achieve high SSD performance by writing host data at the SLC speed. However, our preliminary studies indicate that the SLC cache can lead to a performance cliff if filled rapidly and cause significant write amplification when data migration occurs during idle times. In this work, we propose leveraging a reprogram operation to address these challenges. Specifically, when the SLC cache is full or during idle periods, a reprogram operation is performed to switch used SLC pages to TLC pages in place (termed In-place Switch, IPS). Subsequently, other free TLC space is allocated as the new SLC cache. IPS can continuously provide sufficient SLC cache within SSDs, significantly improving write performance and reducing write amplification. Experimental results demonstrate that IPS can reduce write latency and write amplification by up to 0.75 times and 0.53 times, respectively, compared to state-of-the-art SLC cache technologies.