DNA does change. There are "point mutations", for example, in which say a single nucleotide changes, say from guanine to cytosine. . . . CTG TCA . . . becomes . . . CTG GCA . . . If there is a strand of DNA that suffers such a change, is it then not the same strand of DNA? This is exactly like the question whether persons become different persons if they lose say half a finger. And now we have the problem of DNA identity. When are two descriptions sufficiently similar to count as descriptions of the same strand of DNA? Anthony Quinton has the general issue right, in a 1962 article in the Journal of Philosophy called "The Soul": 'No general account of the identity of a kind of individual thing can be given which finds that identity in the presence of another individual thing within it. For the question immediately arises, how is the identity through time of the identifier to be established? It, like the thing it is supposed to identify, can present itself at any one time only as it is at that time. However alike its temporally separate phases may be, they still require to be identified as parts of the same, continuing thing.' By the way, 6% of identical twins do not have identical DNA, so the members some pairs of identical twins would be metaphysically identical and some would not.
There are several sense to the word "life", which derives from a Norse word having to do with the body; in German we have Leib, body. (1) There is a biological sense, which used to be taken to say that things possess life only if they possess respiration, excretion, reproduction, growth, irritability - I like this one - and cells. Locomotion is also characteristic of animal living things. Physiological life is life in this sense. (2) Life can also be taken to be consciousness or psychological life, so that only conscious beings have life; but I think that this should be taken to mean that only conscious beings have a life. Grass is alive, practically eternal, but it does not have a life, and we do not say that the different kinds of grasses lead separate lives because they don't lead lives at all. A derivative sense here is a life, meaning a biography, as in "A life of Churchill". A life in this sense is a book. (3) "Life" can also mean "way of life", so habits, customs and attitudes, as in "the French way of life", and there is also the unappealing idea of a "lifestyle". "Life" here has a cultural and historical sense. "Life must go on", we say, after a war for example. (4) A life can also be a period of time. So my life started in 1951, and will probably end before 2051. "Life insurance" has to do with this sense, I think, though as we all know what you insure against is the thing insured, so that life insurance should really be called death insurance, as accident insurance is insurance against accident. (So-called house insurance is typically insurance against damage to a house and its contents.)
Perhaps it is only in the first of these four senses that there is anything which makes life to be life - as if it could be anything else! I mean that the seven characteristics (to which more recently are added an eighth characteristic - possession of DNA) are taken to make something which would otherwise be dead or non-living into a living thing. But it is not life which is made to be life by these things; rather it is a being or thing which they are said to make to be living.
In the other senses though what makes life life is just that it conforms to the definition, whatever that is. Though there would be no conforming to the psychological and cultural senses without living (unavoidable, more or less, in the psychological sense), there is an extended sense - living well - in which living badly is said to be no life at all. "Get a life", we say, and it can be a cruel saying or merely a hard one.
There may be as well a sense, though one very hard to grasp, in which "life" coincides with existence or world, so that the meaning of life has the sense of the meaning of existence. What I'm amazed at when I am amazed at the existence of life may be the existence of my life, but it may also be amazement at the existence of the world. 'The World and Life are one. Physiological life is of course not "Life". And neither is psychological life. Life is the world', Wittgenstein wrote in Notebooks 1914-1916. Here there is a sense of "true Life", the true Life, which means something one can live and participate in, no doubt, but more - what more is hard, or harder, to grasp.