Hi,
I would love to help you customize your theme, I hope I do not have to write extra plugins, If that is the case, price could go higher, but just for modifying the theme, yeah It can be done. Also the duration depends on the changes that is required.
Since there is no specific changes mentioned, It could be a very simple changes so I have put 0 days as it could be modified in few minutes.
I can have a fully custom WP theme developed in like a day or two based on the complexity of the theme. So yeah I can modify WP themes.
If you are interested. do let me know
Looking forward to help you modify your WP theme.