Which flavour of unix you are using.
for solaris if you want to change your prompt
echo $PS1 will tell you the prompt.
you neet to type
PS1=#
or
PS1=@

or
PS1="`hostname`{`logname`}"
whatever you want.Then execute the coomads whichever you want.

then press ^d you will be taken out of that shell.
you will again prompt to the original shell.

Thanks
Namish