#as per usual...

thank you very much for the ask, anon!

what tom jr.'s life would have been like if tom sr. had raised him is something i've had a couple of other asks for, so that's coming at another time.

but on the name thing:

i do think that the riddles would probably have changed wee tom's name... because "tom" is a diminutive. tom riddle sr. would legally have been "thomas", and his nickname would only have been used among close friends or family.

the norms on this have changed a lot in the past thirty-or-so years - and diminutives [including, of course, "harry"] are now widely used in britain as standalone names by all social classes - but in the 1920s it would have been thought of as extremely vulgar for a child to be legally named "tom" or "tommy" instead of "thomas".

[which is an important character detail about the canonical voldemort - he's not just legally "tom" in order to make the anagram work. it's yet another thing which marks him out as working-class among his peers at hogwarts.]

so tom jr. would definitely be upgraded to thomas, at the very least. the riddles might also consider changing his name altogether - although it's worth saying that it wouldn't automatically signify anything for him not to be named after his father [that is, tom sr. might not want his son to share his name because the idea has negative connotations for him, but nobody outside of the family would realise this]. it's much, much less common in britain - both historically and today - for firstborn sons to be named after their fathers than it is in other parts of the world, even in the [non-royal - it's more common among royalty for the establishment of dynastic mystique] upper-classes.

what is common among families from the riddles' class-background is choosing from a fairly tight selection of names which turn up across the generations.

so, let's say that tom sr. is thomas william edward riddle - and his father is william robert george riddle - and his grandfather was robert james edward riddle - and his great-grandfather was thomas george louis riddle... then we have a series of potential names for tom jr. to end up having bestowed upon him.

and i think he would. although not - i think it's worth saying - because keeping the name "marvolo" would indicate anything to wider society that the riddles would prefer to keep hidden. it sounds enough like a surname that this could be what they explained it away as - taking advantage of the fact that merope wasn't around to say otherwise to put about the story that tom jr.'s mother was some sort of exotic beauty ["marvolo" would sound plausibly like an italian surname to many english speakers, for example] who died in glamorously tragic circumstances. including the mother's maiden name as [one of] the child's middle name[s] is a common practice in britain.