Depends on the Mac laptop. Many of the Intel CPU models have replaceable parts. Some don't. The M-series are worse for user-serviceability, but that's true across the board, not just laptops.Reaper is still supported on OSX 10.5 and later. However, not much else is.
If you want to get an older Mac, my advice is to look for a Mini rather than a laptop. Those you can get some parts for (DIMM's & SSD's) but with a laptop you're SOL.
When shopping for an old-stock or used Mac, check iFixit first. It has report cards on the repairability of various products and provide tutorials on how to repair or upgrade individual models. You can use those to inform your decision.
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