The biggest tracking hurdle is to figure out if the ISP that handed out the block of addresses is handing out /64s, /56s, or /48s. The network provided to you is functionally the same as the IP address assigned to you with IPv4.
In theory I could rent an IPv4 /29 (of which 6 addresses are usable) for like 20 euros a month from my home ISP to cause the same confusion but I doubt it'd confuse trackers to use those.
ISPs do, cloud providers often give smaller ranges.
Re: renaming all the prefixes, that's why I use a ULA within my home network. Not as useful if you want your services available from the outside if you move ISPs (NAT66 can help on the inside but you'd still need to update all DNS records to use the new prefix). I'll stick with my ULA + VPN fallback for now, I don't expect the prefix to change more than once every five or six years.
If you want a static prefix with a changing prefix, you're probably better off with getting a Hurricane Electric tunnel. Or if you want to go hard on the IPv6 homelab hobby, get your personal IPv6 address space and a bring-your-own-IP business ISP.
By convention they're supposed to DHCP you at least a /64 if not something wider. I don't believe there's any expectation it be static (although it typically is AFAIK) and there are some providers that defy expectations by handing out narrower slices (up to and including /128).
I thought most ISP's give out at least /64's for free these days? Telia gives out a /56, although unfortunately there's no way to migrate them. This was a big deal for my homelab when I was moving, as I had to manually update all prefixes everywhere. A pain in the ass.