This DEFINITELY doesn't count as Ship of Theseus. All those parts are designed to be replaceable on the Thinkpad.
If you really want to talk about Ship of Theseus-ing a Thinkpad, the hardcore guys have literally ripped out the motherboard and installed a completely different motherboard with a modern i7 CPU. These "frankenpads" include the X62 (Broadwell CPU and motherboard in an old X61), T70 (Kaby Lake CPU in a T60), X210 (Kaby Lake R CPU in a X200 body). They also rip out the LCD and replace it with a modern IPS display. They sometimes also rip out the keyboard to replace it with an older keyboard- T420 keyboard in a T430 is common.
> So, a CPU upgrade? How is that not what OP mentions?
Are you asking how replacing the motherboard in a laptop with a custom third party hobbyist replacement is different from putting a faster CPU in a CPU socket?
This kind of CPU upgrade was all but supported by the manufacturer.
Unlike modern laptops, the T430 motherboard had a socketed CPU (like a desktop motherboard). Upgrading the CPU was only marginally more difficult than upgrading the RAM (as long as the replacement CPU had the same package/pinout and was supported by the chipset). Lenovo datasheets would even give you a table of every CPU configuration they tested.
The "hardcore guys" mentioned by the parent are installing bodged motherboards that were never designed to fit in a given model's enclosure, occasionally doing major board surgery to make it work.
The ram upgrade was common since the 2012s, thinkpad sold 16gbs as an upgrade while buying the laptop at the time. SSDs needing to be upgraded has also been recommended since that time. And the processor update was simply maxing out the processor upgrade from that generation. It was available on the workstation version of the thinkpad in the same generation. The i7-3820QM release date is 04/23/2012. It's still a processor from 2012. A new SSD doesn't mean current gen speeds, the internal and the caddy are still limited to sata 3 speeds. It's a very 2012 machine, a very nice 2012 machine and still lacking a dedicated GPU.
There were reasonably fast laptop SSDs in 2012. I had the intel one In my x61 and x201 thinkpad. The specific components though may be faster, then again the newer SSDs would be bottlenecked by the motherboard bus. Sourcing newer models would be a matter of logistics, not performance improvement. Same with RAM. CPU improvements have also been marginal in my opinion, for intel chips, depending on your workload. I was running photoshop professionally just fine, video maybe not so much.
If you really want to talk about Ship of Theseus-ing a Thinkpad, the hardcore guys have literally ripped out the motherboard and installed a completely different motherboard with a modern i7 CPU. These "frankenpads" include the X62 (Broadwell CPU and motherboard in an old X61), T70 (Kaby Lake CPU in a T60), X210 (Kaby Lake R CPU in a X200 body). They also rip out the LCD and replace it with a modern IPS display. They sometimes also rip out the keyboard to replace it with an older keyboard- T420 keyboard in a T430 is common.