Yes, it absolutely can be done.
Unfortunately, usually at a higher cost than simply selling the existing rifle and buying a Colt from scratch. I've done the former, twice, and I love those rifles, but the resale value on them is nowhere near what I put into them, so I've written off most of that sunk cost as the price of learning the whole buy once cry once rule.
When even eating the cost of reselling what you already have and paying MSRP puts you ahead, don't feel bad about it, that's just how it is. It doesn't cost a whole lot more to do the QC/QA to make a rifle top tier, but that kind of stuff adds up, and is why an RRA/Bushhampster/DPMS type rifle is only one or two bills cheaper than a top of the line one.
عندما تصبح الأسلحة محظورة, قد يملكون حظرون عندهم فقط
کله چی سلاح منع شوی دی، یوازي غلوونکۍ یی به درلود
"Being able to do the basics, on demand, takes practice. " - Sinister