Depends on what you mean by "Can I"
If you're asking if you have the ability (i.e. skills) to do the repair, only you can answer that.
If you're asking if you're permitted to do the repair, that may depend on the device. In my case, the answer would be yes as no one is going to stop me, not even the manufacturer of the router. Not only can I repair or upgrade my router (e.g. upgrade heatsink for better cooling and performance), but I can also flash it with a custom firmware (e.g. Tomato, Asuswrt-Merlin).
Unlike Apple, where iOS checks to see if a replacement part is OEM or not, or you're prevented from installing a different OS, Asus doesn't do anything like that or tries to stop people from tinkering.
Ah, tinkering, the thing that Steve Jobs and Steve Wozniak did in a garage back in the early 1970s that led to the creation of Apple Computer Inc. Imagine if things were as locked down then as they are now. Where would we be?
Hard prevention methods for alternate operating software in a smartphone is a different discussion than non OEM part replacement. Further, you compared an ASUS to a smartphone. No, That’s incongruous. Compatible comparison is of a MacBook with an ASUS. Both can run Windows, both can run Linux, one can run MacOS (running windows or Linux on a MB not a fun journey but it can be done), tinker-ability possible for both though very notably more on ASUS. (M1 MB may be an exception)
Using some non OEM parts in an iPhone, such as a battery, can be done. Does iOS (ummm, after 12?) check and give a warning, yes. Does the phone quasi-brick itself, no. Does it send a code red to Apple’s Parts Enforcement System (A.P.E.S.) for having a RonCo battery? No it doesn’t. Is a company wrong to alert a user that it’s not OEM parts in their very expensive smartphone? No, the Vast amount of users aren’t of the tinkering skill club and may (or may not) appreciate warnings especially when they’ve purchased a very premium brand such as Apple. That is a manufacturer’s call. (Btw, Linux on iPhone can be done)
You are permitted and no one is stopped from tinkering on any device they buy and outright own (APES is not summoned to your house). Take out your ohm meter, tweaker(a must have), needle nose, dykes, anti static strap and fire away (if newer you’ve likely voided the warranty but that is SOP for many, not just an Apple thing). Make better iPhone hardware in your garage, you’ll be MR famous if nothing else. Until then, is your contention that Apple modulates the iPhone final assembly more than other manufacturers, and you don’t like it? It needs to be stopped? You want the freedom to break it down below sub assembly components? Well Good news, get Back in that garage because you can do that also. You’ll need serious skills and some precision tools just to make it something more than the bride of iPhone Frankenstein. But if you’re invoking the Two Steves in their garage band days? You maybe can do this!
It sounds as if you’re not a fan of the Apple way: extra modulated, lock down os, over limit how a user can get themself in ‘trouble’, premium price etc etc. Nothing wrong with that. My issue is that some that share your view believe Apple must accommodate them. There’s lots who do like that way. Either way the accommodation is just not gonna happen.