I disagree. You should not immediately go and replace the OS as soon as you get it.

Most modifications to the root filesystem persist through updates just fine. You simply need to add the relevant exclusions for your customizations. See the Development and Modding section here.

I have a significant amount of modifications to Steam OS, including an encrypted home partition (while excluding the steamapps subdirectory via bind mount) protected by TPM.

The only time an update breaks anything is if the kernel or initramfs updates, requiring me to re-enter the LUKS password and reenroll a new TPM protector. And this is only because they don’t support Secure Boot, so my PCR selection is limited. And I was on the Beta update channel for a while updating almost weekly without issue.