Order 6 rule 17

For amendment in pleadings ( plaint and written statement) provision of order 6 rule 17 cpc is proper and applicable, your application under the provision of order 6 rule 17 cpc  is perfectly right and maintainable. sec 151 deals with inherent powers of court is invoked in specific circumstances.

There is no requirement to mention Section 151 CPC (inherent powers of the court) when there is specific provision to amend your plaint, which you have rightly quoted i.e., Order VI Rule 17 CPC.

However, can you explain qua Rule 28 CRP as mentioned by you for my / our knowledge?

It is not mandatory to invoke the provisions of section 151CPC when you you have already invoked proper provision.

Better mention section 151 of cpc in your application to take advantage of inherent power of court. 

What is your locus standi to the suit ?

Section 151 of CPC is to be invoked when there is no specific provision of law. Since, there is specific provision relating to amendment of pleadings as provided by Order VI Rule 17 of CPC, there is no requirement to invoke section 151 CPC in the present case.