CRISPR in its current state do not allow for efficient and 'scar-less' recombineering. Too many off-targets, you can not really force HDR over NHEJ and God forbid MHEJ. It is possible to synthesize oligos rather long (Let's say 3Kb). It's called gBlocks, it's expensive and because of them retards :
https://www.sciencemag.org/news/2017/07/how-canadian-researchers-reconstituted-extinct-poxvirus-100000-using-mail-order-dnaIt's really restricted. As in : You have to be part of a lab and sign a document stating that you are not synthesizing any toxins, viruses blah blah blah.
But: There's always a workaround...
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