I would like to use one of the ecommerce application (preferably opencart, for its slick design).
But most of them have a common problem to me - I cannot change the word 'quantity' per category I want to build. It has to be modified a little.

For example, selling a domain name would have 'quantity' as a 'number of years to buy' for.
In this case, a maximum number of years a customer can purchase is 10.
It means, it does not allow to buy multiple domains. Nor it allows a domain to exceed 10 years.
(A case of maximum quantity limit per product per purchase.)

Similarly a 'service sale' of 'networking the computers' might need 'quantity' as number of 'network ports' to install.

And selling unit of network cable is in 'meters'.

So, the word - quantity - does not fit well for me.
Do you have any ideas on this issue?
And also suggest what ecommerce application to use in order to address such issues?