Hi,
Generally, it should be possible to override/edit any component in the DSpace 7 themes. However, for more complex changes, it requires more complex Angular coding practices. The overall approach is described in the documentation at
https://wiki.lyrasis.org/display/DSDOC7x/User+Interface+Customization However, that does *not* get into more complex changes. There are some comments at the bottom of that page providing some examples of more complex changes. Other examples can be found in past webinars on customizing DSpace such as this one:
https://wiki.lyrasis.org/display/DSPACE/2022-11+-+DSpace+7.4+Webinar+Series
I'd also highly recommend working with DSpace 7.6 (or 7.6.1) if possible. DSpace 7.0 had a slightly different theming structure than later releases, so a theme built for 7.0 may not work properly in 7.6 (it will require updates whenever you upgrade). It'd be better to start with 7.6.x if you can.
If you need more specific help, then I'd recommend sharing more information about the errors you've received. You may also wish to move this discussion to our developer list at
https://groups.google.com/g/dspace-devel since it seems to be a development question.
Tim