The general answer to your question is yes, but not quite in the way you planned. This is from the IRST documentation on using SRT, or Accelerating the Storage System:
If the solid-state drive used as a cache device is larger than 64 GB and has a minimum of 4 GB of additional space, a second single-disk RAID 0 volume will be automatically created using that space for simple data storage.
It sounds like you may have never created an Intel RAID volume, and SRT or SSD caching is a special type of RAID. It still performs some of the standard things that happen when RAID volumes are created.
When the SSD is selected as the cache device and configured, it will be formatted and its contents lost. You cannot partition it in advance, nothing will be preserved when the SSD becomes a caching device.
The usual way to use SRT is to install your OS on a HDD, and then use a SSD to accelerate the system.
You can't decide later to use the SSD for caching, as you mentioned if the SSD fills up, at least without first creating an image of the SSD, and use that to recreate your OS, etc, on a HDD. That HDD then becomes your OS/C: drive, and you then use the SSD as its cache. You will also have whatever space remains on the SSD after you choose the size of the cache (64GB max) as a separate volume.
It's easiet to set the SATA mode in the UEFI/BIOS to RAID before you install your OS on a new system, and install the Intel IRST driver for your board. You can then run the IRST GUI, open the Help section, and read the Accelerating the Storage System section, which explains how it is all done, and the options you must configure. I would not try to set up an accelerated storage system without reading the documentation.