Grep 2 consecutive lines and replace the second line in a file

Shell Programming and Scripting
1

I have a file lake this

cat ex1.txt

</DISCOUNTS>
		<B2B_SPECIFICATION elem="0">
			<B2B_SPECIFICATION elem="0">
				<DESCR>Netti 2 </DESCR>
				<NUMBER>D02021507505</NUMBER>
			</B2B_SPECIFICATION>
			<B2B_SPECIFICATION elem="1">
				<DESCR>Puhepaketti</DESCR>
				<NUMBER>D02021507505</NUMBER>
			</B2B_SPECIFICATION>
		</B2B_SPECIFICATION>
</SUBSCRIPTION_LABEL>

Hi

i want to grep 2 consecutive occurrence of <B2B_SPECIFICATION elem="0">
and first line should be replaced with <B2B_INFO>

like this

</DISCOUNTS>
		<B2B_INFO elem="0">
			<B2B_SPECIFICATION elem="0">
				<DESCR>Netti 2 </DESCR>
				<NUMBER>D02021507505</NUMBER>
			</B2B_SPECIFICATION>
			<B2B_SPECIFICATION elem="1">
				<DESCR>Puhepaketti</DESCR>
				<NUMBER>D02021507505</NUMBER>
			</B2B_SPECIFICATION>
		</B2B_SPECIFICATION>
</SUBSCRIPTION_LABEL>
2

Hi,
Are you sure that it's sufficient ?
You don't need change close tag ?

<B2B_INFO elem="0">
...
...
</B2B_SPECIFICATION>

Regards.

3

And, which one should be processed, the one from the title

(and I doubt it's the 2. in file as there should be at least one with <DISCOUNTS>)
or the one from your spec