It's not physically impossible to change the hardware, software, or batteries of any Apple product, it's just not designed to accomodate that. By selling a separate OS to multiple different PC vendors, Microsoft actually employed the exact opposite tactic, and that hasn't exactly been an unvarnished success.

It's counterfactual to speculate on what Apple might have done if they won the PC war. The fact remains that Microsoft abused their monopoly to undermine Netscape and Java and stole the source code to Quicktime.