As CACHE replacement can be connect to ZX-BUS external interface with memory. But what is ROM type priority in russian clones ? IF trdos rom is connect, can external device disable this rom and connect in low 16kB extra ram pages ?

On all ZX Spectrum machines is it possible (any rom page can be disabled and replaced from external device in any time)

Using ram with selectable write protect in low 16kB is very very cool.
It can copy rom pages to sram with possibility rewriting.
This interface (external CACHE) can be connect to any other ZX clone with compatible ZX-BUS and don't need any hardware modification.
I can design this interface for russian ZX clones (based on one CPLD + SRAM + battery)

this is my old external memory 1MB sram with battery backup and selectable writeprotect:
http://velesoft.speccy.cz/prodej/prodej4/mb02-mem.htm