さも自分は当事者で真相を知っているかの如く、新しい奇怪な物語を描き、
I always wondered if it was possible to replace である with で, is it what that is? 当事者である真相を知っているかの如く、
Furthermore, I'd like clarifications regarding two other things:
1- How would you translate さも in this case? 2- Is かの如くsomething working by itself? It reminds me of かのように
「さも自分{じぶん}は当事者{とうじしゃ}で真相{しんそう}を知{し}っているかの如{ごと}く、新{あたら}しい奇怪{きかい}な物語{ものがたり}を描{えが}き、」
This 「で」 is explained here:
How to parse 中国人で日本語が話せる方は、お電話ください。
I always wondered if it was possible to replace である with で, is it what that is?
No, it is not, but you almost got it. In meaning:
「で」＝「であり」 and not 「である」
That is because 「である」 is in the terminal form, with which you can end a sentence. 「で」 and 「であり」 are both in the continuative forms.
1- How would you translate さも in this case?
"as if"
2- Is かの如くsomething working by itself? It reminds me of かのように
It can work by itself, but in this case, it works in conjunction with 「さも」.
「かの如く」 means the same thing as 「かのように」. Only, the former is more formal than the latter.
"As if (someone) were the party concerned and knew the truth, s/he would create new and uncanny stories and..."
「当事者である彼は真相を知っている」 <- Here, 当事者である is a relative clause modifying 彼. It's「である+noun」. You can't rephrase it as 「当事者で彼は真相を知っている。」. You could say 「彼は当事者で、真相を知っている」or 「彼は当事者であり、真相を知っている」. You use 「で/であり+verb phrase or another clause」.
当事者である真相を知っているかの如く doesn't make sense because である is attributive and modifies a noun (or noun-like phrase) right after it. In this case, 当事者である真相 would mean "the true fact that (someone) is a person involved" (i.e., the fact that he was involved was not known), which is not what the sentence wants to say.
Instead, you can use the continuative-form/連用形 and say:
さも自分は当事者で真相を知っているかの如く、...
さも自分は当事者であり真相を知っているかの如く、...
as if he were a person involved and knew the truth ...
Using であり can make the sentence look literary or stiff, but in this case it doesn't matter because さも and 如く are already fairly stiff wordings.
さも is a literary adverb that is used with ～ように/～そうに/～ごとく/etc to mildly intensify its meaning. You can translate is as "really (like)" or "indeed" if you need to, but you may ignore it.
For 如く, please refer to Usage of 如き, 如し, 如く.
