If you modify a form letter before sending it back without notifying the other party of the changes, I'd say it's reasonable that the contract is either invalid or should be treated as unmodified.
You only have to notify people of a change, if it's already signed (and generally that's because your contract will have some form of amendment system that involves notification).
I've been through many B2B negotiations, many of them reaching awful levels of yelling, but the lawyers always red-lined their changes as they undid other side's changes dozens of times.
Akamai's abuse on this front is the reason that we stopped trusting 'track changes' and started doing full-text diffs.
I'm sure it happens. This says nothing about whether these actions would hold up in court, though.
Don't make the classic programmer's mistake of expecting everything in the law to need to be as well defined as things are in mathematics. Judges will quite happily decide what a term means on the fly, consistent with precedent and reasonableness, to stop you getting away with anything completely ridiculous.
But in fact there is so much subtlety and nuance to it that I don't understand how computers could ever do it. I mean, you're trying to persuade a human being that your version of the facts is more compelling than your opponents. Last time I checked computers were not very persuasive orators or writers....
It is not the receiving party's responsibility to determine if something they receive is another party's form letter, or other spam-like.
It seems like you are requiring some out-of-band signalling? What should the specs be for that other signalling mechanism?
My guess is that he filled out the application forms, set the terms of the contract how he desired them, left a note on top of it all to the effect of, "BTW, I changed the terms, lol. You should probably read them.", stuffed it in an envelope and mailed it to the bank. A bank clerk probably received the envelope, looked to make sure the application form was filled out and the contract signed, then marked in the bank's database that the requisite documents had been received.
From the article it's not entirely clear to me what form his modifications took:
> [He] scanned it into his computer, altered the terms and sent it back to Tinkoff Credit Systems.
By this do they mean he did something like "photoshop" the scanned contract, producing a result that looks as similar as possible to the original, but with some parts digitally modified? That would be a bit more misleading, if so.
In the UK for instance, if you're changing credit card terms, you'd be expected to send a notice of variation looking something like this (https://www.hsbc.co.uk/content_static/en/pdfs/en/nov_general...)