The short answer is no.
The long answer is that the Rolleicord lens with the scratch has 75 millimetres written on it as the focal length. But it's not really 75mm. It may be 76.45 mm, or 74.75 mm or some other near focal length.
The viewing and taking lens of a quality TLR will have two lenses that have been measured for focal length and matched exactly from the makers stock. This is the only way that the focus accuracy can be optimum all the way through the minimum focus distance to infinity. If the focal length is not identical you might get the lenses to coincide over part of the focus range but they will not be as good as a factory matched set.
It gets harder. When lenses are being manufactured they will of course begin as blanks that are ground to the correct profile and assembled as a complete lens, being cemented together in many cases depending on the lens design. With any manufacturing process no matter how high quality there are always deviations from the theoretically perfect profile and tolerances for these. One of the ways a lens manufacturer can achieve the best possible performance of their optics is by selecting various elements that together work as well as possible by complementing the characteristics of the other pieces. How much this is the case in modern lens manufacture I can't say, but in the pre-computer age during which these lenses were manufactured this was assuredly one of the ways in which best possible results with the technology of the time were attained.
Hence, the problem surrounding substituting a lens component with a flaw (usually, but not always, the front glass) is twofold. Not only will Eg. exchanging a whole taking lens assembly create inaccuracies due to the very high likelihood that the focal lengths will not agree. But simply changing a part of your damaged taking lens, such as the front group of the Xenar (I assume it is a Xenar, not a Triotar, because you haven't bothered to tell us) is probably an even worse idea than swapping a complete lens. Not only will it impact the focal length of the assembled franken-lens but it's not going to make its sharpness better than before (well it's theoretically possible but highly unlikely).
You are really going to have to live with the performance of the lens as it is and work within its limitations (you have a hood, I assume?) or source a complete set of factory matched viewing and taking lenses from a donor camera to achieve a level or performance that, realistically, is likely to be as good as factory. Either that or obtain the services of a professional repairer with an optical bench to do the necessary checks needed to ensure that any substitution of parts otherwise considered performs to an acceptable standard.
Generally speaking it is a really bad idea to mix and match lens parts from different cameras. Regrettably some sellers do precisely this and it is usually impossible for anyone who might purchase such a camera in good faith to spot this, leaving them to wonder why their neat and tidy Rolleicord or Rolleiflex doesn't render very sharp pictures. In the process at least one viable camera and perhaps two are compromised. It tends to upset a lot of Rollei enthusiasts, too, who, understandably, get a little ticked off about people buggering up what might be an otherwise usable camera...
Cheers,
Brett
